A heterogeneous ozone catalyst with a dual active site and a preparation method and application thereof

Abstract

The present application relates to the technical field of ozone catalytic oxidation, and particularly relates to a heterogeneous ozone catalyst with double central active sites, a preparation method and application thereof. The heterogeneous ozone catalyst comprises a catalyst substrate with a porous structure; iron oxide is dispersed in the catalyst substrate; and a transition metal oxide is loaded on the inner surface of the pore of the catalyst substrate, wherein the transition metal oxide comprises one or more of cobalt oxide, manganese oxide, nickel oxide and copper oxide. The present application utilizes two active centers dispersed in the catalyst substrate and loaded on the pore surface respectively, so as to overcome the shortcomings of the single distributed metal active oxide, such as insufficient catalytic performance or performance rapid decline caused by loss during operation, and the two active centers respectively adopt specific metal oxides, so as to better cooperate and achieve higher catalytic activity.

Description

A heterogeneous ozone catalyst with dual-center active sites, its preparation method and application Technical Field

[0001] This invention relates to the field of ozone catalytic oxidation technology, and in particular to a heterogeneous ozone catalyst with dual-center active sites, its preparation method, and its application. Background Technology

[0002] Ozone catalytic oxidation technology, as a novel and green advanced oxidation technology for wastewater treatment, boasts advantages such as high efficiency, environmental friendliness, and no secondary pollution, and has been widely used in the deep treatment of industrial organic wastewater. In the ozone catalytic oxidation system, ozone reacts with the active center of the catalyst to transform into hydroxyl radicals (·OH) with higher redox potential. These active species can indiscriminately degrade large-molecule organic pollutants into smaller-molecule substrates and further thoroughly mineralize them into inorganic CO2 and H2O. This not only significantly reduces the COD value of the treated wastewater but also improves the B / C ratio, making it more conducive to subsequent biochemical treatment.

[0003] As the core of the ozone catalytic oxidation process, the catalyst's high catalytic efficiency and long service life are important indicators of its performance. From the perspective of the catalyst itself, on the one hand, the activity of an ozone catalyst mainly depends on the type, distribution, and number of active centers; on the other hand, the stability of an ozone catalyst is mainly affected by the pore structure and the number of active centers. Currently, the active centers of ozone catalysts widely used in industry are mainly transition metal (hydrogen) oxides, such as Fe₂O₃, γ-FeOOH, CuO, MnO₂, and Co₂O₃. These metal oxide active components are either supported on porous adsorption media (such as alumina spheres or activated carbon particles) through impregnation, co-precipitation, etc. (i.e., single-supported ozone catalysts), or directly combined with mixed oxides through spheroidization (i.e., single-mixed oxide ozone catalysts).

[0004] In the application of the aforementioned single-supported ozone catalysts (such as patent CN111841554A), the highly dispersed metal oxide active centers distributed on the inner and outer surfaces of the catalyst will inevitably be lost, leading to a decrease in the ability to activate ozone and a shortened catalyst lifespan. In single-mixed oxide ozone catalysts (such as patent CN115090319A), although the metal oxides are uniformly distributed in the catalyst matrix, effectively suppressing the loss of active components, most of them exist in the form of highly aggregated micro-nano particles. Their ability to catalyze the oxidation of ozone to form active free radicals is significantly lower than that of highly dispersed supported catalysts, and the corresponding degradation efficiency of organic pollutants in wastewater is also lower. Summary of the Invention

[0005] To address the technical problem of low catalytic activity in existing ozone catalysts, this invention provides a heterogeneous ozone catalyst with dual-site active sites, its preparation method, and its applications. This heterogeneous ozone catalyst utilizes two types of active sites, one dispersed in the catalyst matrix and the other supported on the pore surface. This overcomes the shortcomings of insufficient catalytic performance or rapid performance degradation caused by the loss of single-distributed metal active oxides during operation. Furthermore, the two active sites are each composed of specific metal oxides, allowing for better synergy and achieving higher catalytic activity.

[0006] The specific technical solution of this invention is as follows:

[0007] In a first aspect, the present invention provides a heterogeneous ozone catalyst with dual-center active sites, comprising a catalyst matrix having a porous structure; iron oxide is dispersed in the catalyst matrix; and transition metal oxides are loaded on the inner surface of the pores in the catalyst matrix, wherein the transition metal oxides include one or more of cobalt oxide, manganese oxide, nickel oxide, and copper oxide.

[0008] In the heterogeneous ozone catalyst of the present invention, the active centers with different distributions include iron oxide dispersed in the matrix and transition metal oxides supported on the inner surface of the pores. After ozone diffuses into the interior of the pores, it will be activated by the iron oxide and transition metal oxides at the above-mentioned different positions to form hydroxyl radicals, thereby promoting the oxidative degradation of organic matter. By utilizing the above two specific distributions of active centers, on the one hand, the high dispersion of active centers supported on the inner surface of the pores can be utilized to enhance the catalytic activity of the catalyst; on the other hand, the active centers dispersed in the matrix can be utilized to effectively avoid the decrease or complete loss of catalytic activity of the catalyst due to the loss of active centers on the inner surface of the pores or the blockage of the catalyst pores.

[0009] Furthermore, this invention employs iron oxide as a mixed-type active center dispersed in the matrix, and uses one or more of cobalt oxide, manganese oxide, nickel oxide, and copper oxide as a supported active center loaded on the inner surface of the pores, which can produce the following effects:

[0010] (1) The iron oxide dispersed in the matrix is ​​exposed on the inner surface of the pores and can serve as a loading site for transition metal oxides. After high-temperature treatment, the two can form a strong interaction force through metal-oxygen bonds, which can enhance the anti-loss ability of the active center of the supported transition metal oxide. At the same time, the d electron orbitals of iron oxide and transition metal oxides superimpose each other, which can accelerate the electron transfer rate of the reaction system, promote the redox reaction cycle of the system, and synergistically improve the catalytic degradation efficiency.

[0011] (2) Iron oxide dispersed in the matrix can interact with ozone molecules through empty orbitals, thereby enriching ozone molecules on the inner and outer surfaces of the catalyst, increasing the effective ozone concentration in the reaction system, thus promoting contact between ozone and the active centers of iron oxide and transition metal oxides, forming more active free radicals, and thus increasing the rate of ozone catalytic oxidation reaction.

[0012] The invention team discovered that changing the type of metal oxides of the two active centers affects the synergistic effect between them, resulting in poor overall catalytic activity of the heterogeneous ozone catalyst.

[0013] The catalytic mechanism of the heterogeneous ozone catalyst of this invention is shown in Figure 1, where M1xOy is iron oxide and M2xOy is the "transition metal oxide" (one or more of cobalt oxide, manganese oxide, nickel oxide, and copper oxide) described in this invention. The hydroxyl groups (M-OH) contained in the active centers of the metal oxides with different distributions catalyze the ozone oxidation reaction through the following reaction mechanism:

[0014] (1) O3 + M-OH → M-HO2 - +O2;

[0015] (2)O3+M-HO2 - →OH·+O2 ·- +O2;

[0016] (3) O3+O2 ·- →O3 ·- +O2;O3 ·- +H + →HO3 ·- ;HO3 ·- →OH·+O2;

[0017] (4)RH+OH·→R·+H2O; R·+O2→ROO·→ROOH→ROO - →…→CO2+H2O;

[0018] Among them, formulas (1) and (2) are the activation of ozone by metal hydroxyl functional groups to form hydroxyl radicals, formula (3) is the formation of free radical chain reaction, and formula (4) is the activation of organic matter by hydroxyl radicals to form organic matter free radicals and a series of subsequent oxidative degradation and mineralization reactions, ultimately achieving deep degradation of organic pollutants.

[0019] Preferably, in the multiphase ozone catalyst, the contents of iron oxide and transition metal oxide are 5.0–10.0 wt% and 2.2–3.8 wt%, respectively.

[0020] To a certain extent, increasing the content of transition metal oxides can improve the catalytic activity of heterogeneous ozone catalysts. However, since the iron oxide active centers in this invention can serve as loading sites for transition metal oxides, and the two are bonded together through metal-oxygen bonds, excessively high transition metal oxide content can overly cover the iron oxide exposed on the inner surface of the pores, thus causing a decrease in the catalytic activity of the heterogeneous ozone catalyst. Therefore, this invention, with an iron oxide content of 5.0–10.0 wt%, controls the transition metal oxide content within the range of 2.2–3.8 wt%, which further enhances the catalytic activity of the heterogeneous ozone catalyst.

[0021] Preferably, the catalyst matrix comprises iron oxide, silicon dioxide, and aluminum oxide.

[0022] Furthermore, in the multiphase ozone catalyst, the contents of silica and alumina are 10.0–15.0 wt% and 74.5–80.4 wt%, respectively.

[0023] Preferably, the multiphase ozone catalyst has the morphology of columnar or strip-shaped particles with a bulk density ≥1.25 g / cm³. 3 The particle diameter and length are both 3.0-5.0 mm, and the compressive strength is ≥150 N / particle.

[0024] Due to limitations in catalyst morphology and material, the bulk density of most existing catalysts is ≤1.0 g / cm³. 3 For example, the packing density of existing aluminum-based spherical ozone catalysts is generally 0.7–0.8 g / cm³. 3 Therefore, in order to achieve a certain organic pollutant removal efficiency, the reactor volume needs to be significantly increased to meet the filling quality requirements, which will increase the investment costs of equipment and site.

[0025] The present invention designs the multiphase ozone catalyst into columnar strip particles, which can increase its bulk density and reduce the volume and footprint of water treatment devices compared to spherical ozone catalysts.

[0026] Secondly, the present invention provides a method for preparing the heterogeneous ozone catalyst, comprising the following steps:

[0027] (1) Mix the catalyst matrix raw materials, including iron oxide source, and add adhesive to knead to obtain premix;

[0028] (2) The premix is ​​shaped, dried and calcined to obtain a catalyst matrix containing iron oxide;

[0029] (3) The catalyst matrix is ​​placed in a transition metal salt solution, fully impregnated, dried, and then calcined to convert the transition metal salt into a transition metal oxide, thereby obtaining a multiphase ozone catalyst.

[0030] Preferably, in step (1), the iron oxide source is iron oxide and / or iron hydroxide, and its content in the catalyst matrix raw material is 3.5 to 15 wt%.

[0031] Preferably, in step (3), the concentration of the transition metal salt solution is 0.05 to 0.50 mol / L, the mass-to-volume ratio of the catalyst matrix to the transition metal salt solution is 1.0 g: 1.2 to 2.0 mL, and the time for full impregnation is 10 to 15 h.

[0032] Preferably, in step (3), the transition metal salt is one or more of cobalt acetate, manganese acetate, nickel acetate and copper acetate.

[0033] Using acetate as a transition metal oxide precursor can avoid the formation of toxic and harmful nitrogen oxides and hydrogen chloride during the high-temperature decomposition of conventional nitrate and chloride precursors, making the catalyst preparation process more green and environmentally friendly.

[0034] Preferably, in step (1), the catalyst matrix raw material includes the following components in parts by weight: 120-180 parts of activated alumina, 77-120 parts of boehmite, 25-45 parts of glass fiber, 16-35 parts of iron oxide source, and 7-11 parts of pore-forming agent.

[0035] Introducing glass fibers into the catalyst matrix helps to significantly improve the compressive strength of ozone catalysts, effectively overcoming the shortcomings of insufficient strength of conventional spherical catalysts.

[0036] Furthermore, the pore-forming agent includes one or more of citric acid, guar gum powder, and activated carbon.

[0037] The aforementioned pore-forming agents can regulate the pore structure of the carrier and enhance the adsorption behavior of ozone catalysts on substrates (such as organic pollutants in wastewater).

[0038] Preferably, in step (2), the roasting is carried out in an aerobic atmosphere at a temperature of 450-500°C for 3.5-4.5 hours; in step (3), the roasting is carried out in an aerobic atmosphere at a temperature of 400-450°C for 3-6 hours.

[0039] Preferably, in step (1), the adhesive is an inorganic acid adhesive.

[0040] Further, in step (1), the adhesive is a nitric acid solution with a concentration of 3-5 wt%.

[0041] Preferably, in step (2), the forming method is extrusion forming, and the extrusion speed is controlled to be 30-45 r / min.

[0042] The vast majority of existing ozone catalysts are prepared using a spheroidizing process. This process has high requirements for the composition of raw materials, and the range of modulation of the pore structure and specific surface area of ​​the resulting catalyst is limited, which to some extent restricts its high efficiency in degrading different organic pollutant molecules.

[0043] Thirdly, the present invention provides the application of the aforementioned heterogeneous ozone catalyst in the catalytic ozone oxidation degradation of organic matter.

[0044] Fourthly, the present invention provides the application of the aforementioned multiphase ozone catalyst in the treatment of organic polluted wastewater.

[0045] Preferably, the application includes the following steps: filling the multiphase ozone catalyst into a fixed-bed water treatment device equipped with an inlet and an overflow outlet, introducing the organic pollutant wastewater to be treated, and after the wastewater and the multiphase ozone catalyst have been in full contact, performing ozone aeration, and the treated water sample flowing out from the overflow outlet.

[0046] Furthermore, the volume of the multiphase ozone catalyst is 30% to 70% of the effective volume of the fixed-bed water treatment device; the hydraulic contact time between the wastewater and the multiphase ozone catalyst is 25 to 45 minutes; and the ratio of ozone dosage to the concentration of organic matter removed from the water (ΔTOC) is 3 to 9.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] (1) The active centers contained in the multiphase ozone catalyst of the present invention are distributed in the catalyst matrix and the inner surface of the pores, which can overcome the shortcomings of insufficient catalytic performance of single-distributed metal active oxides or the rapid decline in performance caused by loss during operation.

[0049] (2) In the multiphase ozone catalyst of the present invention, specific metal oxides are used in the two active centers respectively (i.e., iron oxide is used as the active center dispersed in the matrix, and one or more of cobalt oxide, manganese oxide, nickel oxide and copper oxide are used as the active center loaded on the inner surface of the pores), which can enable the two active centers to cooperate better and give the multiphase ozone catalyst higher catalytic activity.

[0050] (3) In the multiphase ozone catalyst of the present invention, the contents of iron oxide and transition metal oxide are controlled within a specific range, which enables the transition metal oxide to fully exert its role in improving the catalytic activity of the catalyst and avoids excessive coverage of iron oxide exposed on the surface of the pores, thereby improving the catalytic activity of the multiphase ozone catalyst to a greater extent. Attached Figure Description

[0051] Figure 1 is a schematic diagram of the distribution of active centers and the catalytic activation mechanism of the multiphase ozone catalyst of the present invention.

[0052] Figure 2 shows a 3D optical microscope magnified image of the ozone catalyst. In Figure 2(A), Fe2O3-Al2O3-SiO2 was prepared in Comparative Example 1; and in Figure 2(B), CuO / Fe2O3-Al2O3-SiO2 was prepared in Example 2.

[0053] Figure 3 shows the XRD patterns of the ozone catalysts prepared in Comparative Example 1 and Example 2. Note: In Figure 3, the upper one is CuO / Fe2O3-Al2O3-SiO2 prepared in Example 2, and the lower one is Fe2O3-Al2O3-SiO2 prepared in Comparative Example 1.

[0054] Figure 4 shows the comparison curves of the ozone catalysts prepared in Examples 1-5 and Comparative Examples 1-2 for continuous deep oxidation treatment of actual wastewater from coal chemical industry. Detailed Implementation

[0055] The present invention will be further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0056] General Implementation Examples

[0057] A heterogeneous ozone catalyst with dual-center active sites includes a catalyst matrix with a porous structure; iron oxide is dispersed in the catalyst matrix; and transition metal oxides are loaded on the inner surface of the pores in the catalyst matrix, the transition metal oxides including one or more of cobalt oxide, manganese oxide, nickel oxide and copper oxide.

[0058] In one specific embodiment, the contents of iron oxide and transition metal oxide in the multiphase ozone catalyst are 5.0–10.0 wt% and 2.2–3.8 wt%, respectively.

[0059] In one specific embodiment, the catalyst matrix comprises iron oxide, silicon oxide, and aluminum oxide; in the multiphase ozone catalyst, the contents of silicon dioxide and aluminum oxide are 10.0–15.0 wt% and 74.5–80.4 wt%, respectively.

[0060] In one specific embodiment, the heterogeneous ozone catalyst has the morphology of columnar or strip-shaped particles with a bulk density ≥1.25 g / cm³. 3 The particle diameter and length are both 3.0-5.0 mm, and the compressive strength is ≥150 N / particle.

[0061] A method for preparing the heterogeneous ozone catalyst includes the following steps:

[0062] (1) Mix the catalyst matrix raw materials, including iron oxide source, and add adhesive to knead to obtain premix;

[0063] (2) The premix is ​​shaped, dried and calcined to obtain a catalyst matrix containing iron oxide;

[0064] (3) The catalyst matrix is ​​placed in a transition metal salt solution, fully impregnated, dried, and then calcined to convert the transition metal salt into a transition metal oxide, thereby obtaining a multiphase ozone catalyst.

[0065] In one specific embodiment, in step (1), the iron oxide source is iron oxide and / or iron hydroxide, and its content in the catalyst matrix raw material is 3.5 to 15 wt%.

[0066] In one specific embodiment, in step (1), the catalyst matrix raw material includes the following components in parts by weight: 120-180 parts of activated alumina, 77-120 parts of boehmite, 25-45 parts of glass fiber, 16-35 parts of iron oxide source, and 7-11 parts of pore-forming agent; the pore-forming agent includes one or more of citric acid, guar gum powder and activated carbon.

[0067] In one specific implementation, in step (1), the adhesive is an inorganic acid adhesive; the inorganic acid adhesive can be a nitric acid solution with a concentration of 3-5 wt%.

[0068] In one specific implementation, in step (2), the forming method is extrusion forming, and the extrusion speed is controlled to be 30-45 r / min.

[0069] In one specific implementation, in step (2), the calcination is carried out in an oxygen-rich atmosphere at a temperature of 450–500°C for 3.5–4.5 hours.

[0070] In one specific embodiment, in step (3), the concentration of the transition metal salt solution is 0.05 to 0.50 mol / L, the mass-to-volume ratio between the catalyst matrix and the transition metal salt solution is 1.0 g: 1.2 to 2.0 mL, and the time for full impregnation is 10 to 15 h.

[0071] In one specific implementation, in step (3), the transition metal salt is one or more of cobalt acetate, manganese acetate, nickel acetate, and copper acetate.

[0072] In one specific implementation, in step (3), the calcination is carried out in an oxygen-rich atmosphere at a temperature of 400–450°C for 3–6 hours.

[0073] Application of the heterogeneous ozone catalyst in the catalytic ozone oxidation degradation of organic matter.

[0074] Application of the heterogeneous ozone catalyst in the treatment of organic polluted wastewater.

[0075] As one specific implementation, the application includes the following steps: filling the multiphase ozone catalyst into a fixed-bed water treatment device equipped with an inlet and an overflow outlet, controlling the filling volume of the multiphase ozone catalyst to be 30% to 70% of the effective volume of the fixed-bed water treatment device, introducing the organic polluted wastewater to be treated, and after the wastewater and the multiphase ozone catalyst have been in full contact, ozone aeration is performed, controlling the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water to be 3 to 9, the hydraulic contact time between the wastewater and the multiphase ozone catalyst to be 25 to 45 minutes, and the treated water sample flowing out from the overflow outlet.

[0076] Example 1

[0077] A heterogeneous ozone catalyst with dual-center active sites was prepared by following these steps:

[0078] S1: Weigh out 180g of 300-500 mesh activated alumina powder, 77g of boehmite powder (alumina content 65%), 16g of ferric hydroxide powder, 35g of glass fiber powder, 5.5g of guar gum powder, and 3.5g of activated carbon powder. First, place them in a sealed bag and shake to mix evenly. Then, pour them into a kneading tank and mix thoroughly. After the powders are evenly mixed, continuously add 3.5% dilute nitric acid aqueous solution as a binder and knead thoroughly until a suitable oxide premix with appropriate viscosity and humidity is obtained.

[0079] S2: Slowly add the premixed material into the hopper of the twin-screw extruder, select a cylindrical stainless steel die with an inner diameter of 4.0 mm, control the twin-screw extrusion rate to 40 r / min, and continuously extrude to obtain a cylindrical catalyst precursor;

[0080] S3: The above columnar catalyst precursor particles were air-dried at room temperature for 12 hours, and then transferred to a 90℃ forced-air drying oven for 6 hours. After drying, they were naturally broken into columnar particles of 3.0-5.0 mm and placed in a muffle furnace to be calcined at a constant temperature of 450℃ in air atmosphere at a rate of 5℃ / min for 4 hours to remove guar gum powder, activated carbon and other additives and bound water, to obtain a mixed metal oxide ozone catalyst material with open channels.

[0081] S4: Take the above-mentioned mixed metal oxide ozone catalyst material and place it in a 0.15M cobalt acetate aqueous solution. Perform supersaturated impregnation at a solid-liquid ratio of 1.0g / 1.25mL for 12 hours. After impregnation, filter out the excess impregnation solution to obtain the catalyst precursor. Then, air dry at room temperature, dry at 90℃ for 6 hours, and calcine at 400℃ for 3 hours to decompose the transition metal salt loaded on the inner surface of the pores into metal oxide particles. Finally, a heterogeneous ozone catalyst with dual-center active sites is obtained, labeled as Co2O3 / Fe2O3-Al2O3-SiO2.

[0082] The prepared heterogeneous ozone catalyst contained 2.2 wt% Co2O3, 5.0 wt% Fe2O3, 12.4 wt% SiO2, and 80.4 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.26 g / mL, and the average particle strength was 160 N / particle.

[0083] The obtained heterogeneous ozone catalyst (Co2O3 / Fe2O3-Al2O3-SiO2) was filled into a water treatment device for continuous catalytic oxidation of actual coal chemical wastewater (in all examples and comparative examples, the wastewater used was from the same source and from the same batch, with the same water quality): the hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst filled to 50% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the TOC of the stable effluent was measured to be 33.5 ppm (the change of effluent TOC with operating time is shown in Figure 4), and the mineralization efficiency of organic pollutants reached 60.35%.

[0084] Example 2

[0085] A heterogeneous ozone catalyst with dual-center active sites was prepared by following these steps:

[0086] S1: Weigh out 180g of 300-500 mesh activated alumina powder, 77g of boehmite powder (alumina content 65%), 30g of ferric hydroxide powder, 45g of glass fiber powder, 4.5g of guar gum powder, 2.8g of activated carbon powder, and 3.5g of citric acid. First, place them in a sealed bag and shake to mix evenly. Then, pour them into a kneading tank and mix thoroughly. After the powders are evenly mixed, continuously add a 3.5% dilute nitric acid aqueous solution as a binder and knead thoroughly until a suitable oxide premix with appropriate viscosity and humidity is obtained.

[0087] S2: Slowly add the premixed material into the hopper of the twin-screw extruder, select a cylindrical stainless steel die with an inner diameter of 4.0 mm, control the twin-screw extrusion rate to 40 r / min, and continuously extrude to obtain a cylindrical catalyst precursor;

[0088] S3: The above columnar catalyst precursor particles were air-dried at room temperature for 12 hours, and then transferred to a 90℃ forced-air drying oven for 6 hours. After drying, they were naturally broken into columnar particles of 3.0-5.0 mm and placed in a muffle furnace to be calcined at a constant temperature of 450℃ in air atmosphere at a rate of 5℃ / min for 4 hours to remove guar gum powder, activated carbon and other additives and bound water, to obtain a mixed metal oxide ozone catalyst material with open channels.

[0089] S4: Take the above-mentioned mixed metal oxide ozone catalyst material and place it in a 0.25M copper acetate aqueous solution. Supersaturated impregnation is carried out at a solid-liquid ratio of 1.0g / 1.25mL. After impregnation for 12 hours, the excess impregnation solution is filtered to obtain the catalyst precursor. Then, it is dried at room temperature, dried at 90℃ for 6 hours, and calcined at 400℃ for 3 hours to decompose the transition metal salt loaded on the inner surface of the pores into metal oxide particles. Finally, a heterogeneous ozone catalyst with dual-center active sites is obtained, labeled as CuO / Fe2O3-Al2O3-SiO2. Its optical microscope image is shown in Figure 2(B), and its XRD spectrum is shown in Figure 3.

[0090] The prepared heterogeneous ozone catalyst contained 3.0 wt% CuO, 7.5 wt% Fe2O3, 15.0 wt% SiO2, and 74.5 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.27 g / mL, and the average particle strength was 170 N / particle.

[0091] The obtained heterogeneous ozone catalyst (CuO / Fe2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 25 minutes, the catalyst occupied 70% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 3.5, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the stable TOC of the effluent was measured to be 28.8 ppm (the change of effluent TOC with operating time is shown in Figure 4). The mineralization efficiency of organic pollutants reached 65.91%.

[0092] Example 3

[0093] A heterogeneous ozone catalyst with dual-center active sites was prepared by following these steps:

[0094] S1: Weigh out 120g of 300-500 mesh activated alumina powder, 120g of boehmite powder (alumina content 65%), 35g of ferric hydroxide powder, 25g of glass fiber powder, 2.0g of guar gum powder, 2.3g of activated carbon powder, and 3.0g of citric acid. First, place them in a sealed bag and shake to mix evenly. Then, pour them into a kneading tank and mix thoroughly. After the powders are evenly mixed, continuously add a 3.5% (w / w) dilute nitric acid aqueous solution as a binder and knead thoroughly until a suitable oxide premix with appropriate viscosity and humidity is obtained.

[0095] S2: Slowly add the premixed material into the hopper of the twin-screw extruder, select a cylindrical stainless steel die with an inner diameter of 4.0 mm, control the twin-screw extrusion rate to 40 r / min, and continuously extrude to obtain a cylindrical catalyst precursor;

[0096] S3: The above columnar catalyst precursor particles were air-dried at room temperature for 12 hours, and then transferred to a 90℃ forced-air drying oven for 6 hours. After drying, they were naturally broken into columnar particles of 3.0-5.0 mm and placed in a muffle furnace to be calcined at a constant temperature of 450℃ in air atmosphere at a rate of 5℃ / min for 4 hours to remove guar gum powder, activated carbon and other additives and bound water, to obtain a mixed metal oxide ozone catalyst material with open channels.

[0097] S4: Take the above-mentioned mixed metal oxide ozone catalyst material and place it in a 0.40M nickel acetate aqueous solution. Perform supersaturated impregnation at a solid-liquid ratio of 1.0g / 1.25mL for 12 hours. After impregnation, filter out the excess impregnation solution to obtain the catalyst precursor. Then, air dry at room temperature, dry at 90℃ for 6 hours, and calcine at 400℃ for 3 hours to decompose the transition metal salt loaded on the inner surface of the pores into metal oxide particles. Finally, a heterogeneous ozone catalyst with dual-center active sites is obtained, labeled as NiO / Fe2O3-Al2O3-SiO2.

[0098] The prepared heterogeneous ozone catalyst contained 3.2 wt% NiO, 10.0 wt% Fe2O3, 10.0 wt% SiO2, and 76.8 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.25 g / mL, and the average particle strength was 155 N / particle.

[0099] The obtained heterogeneous ozone catalyst (NiO / Fe2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 35 minutes, the catalyst occupied 65% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 6.0, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the stable TOC of the effluent was measured to be 35.4 ppm (the change of effluent TOC with operating time is shown in Figure 4). The mineralization efficiency of organic pollutants reached 58.10%.

[0100] Example 4

[0101] A heterogeneous ozone catalyst with dual-center active sites was prepared by following these steps:

[0102] S1: Weigh out 150g of 300-500 mesh activated alumina powder, 110g of boehmite powder (alumina content 65%), 30g of ferric hydroxide powder, 25g of glass fiber powder, 2.8g of guar gum powder, 3.5g of activated carbon powder, and 1.0g of citric acid. First, place them in a sealed bag and shake to mix evenly. Then, pour them into a kneading tank and mix thoroughly. After the powders are mixed evenly, continuously add 3.5% dilute nitric acid aqueous solution as a binder and knead thoroughly until the oxide premix has the appropriate viscosity and humidity.

[0103] S2: Slowly add the premixed material into the hopper of the twin-screw extruder, select a cylindrical stainless steel die with an inner diameter of 4.0 mm, control the twin-screw extrusion rate to 40 r / min, and continuously extrude to obtain a cylindrical catalyst precursor;

[0104] S3: The above columnar catalyst precursor particles were air-dried at room temperature for 12 hours, and then transferred to a 90℃ forced-air drying oven for 6 hours. After drying, they were naturally broken into columnar particles of 3.0-5.0 mm and placed in a muffle furnace to be calcined at a constant temperature of 450℃ in air atmosphere at a rate of 5℃ / min for 4 hours to remove guar gum powder, activated carbon and other additives and bound water, to obtain a mixed metal oxide ozone catalyst material with open channels.

[0105] S4: Take the above-mentioned mixed metal oxide ozone catalyst material and place it in a 0.45M manganese acetate aqueous solution. Perform supersaturated impregnation at a solid-liquid ratio of 1.0g / 1.25mL for 12 hours. After impregnation, filter out the excess impregnation solution to obtain the catalyst precursor. Then, air dry at room temperature, dry at 90℃ for 6 hours, and calcine at 400℃ for 3 hours to decompose the transition metal salt loaded on the inner surface of the pores into metal oxide particles. Finally, a heterogeneous ozone catalyst with dual-center active sites is obtained, labeled as MnO2 / Fe2O3-Al2O3-SiO2.

[0106] The prepared heterogeneous ozone catalyst contained 3.8 wt% MnO2, 7.0 wt% Fe2O3, 11.0 wt% SiO2, and 78.2 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.26 g / mL, and the average particle strength was 158 N / particle.

[0107] The obtained heterogeneous ozone catalyst (MnO2 / Fe2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 70% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4.5, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the stable TOC of the effluent was measured to be 31.7 ppm (the change of effluent TOC with operating time is shown in Figure 4). The mineralization efficiency of organic pollutants reached 62.48%.

[0108] Example 5

[0109] The only difference between this embodiment and Example 4 is that the loading of MnO2 in the catalyst is increased, i.e., in step S4, the 0.45M manganese acetate aqueous solution is replaced with a 0.9M manganese acetate aqueous solution; the rest remains the same as in Example 4. A heterogeneous ozone catalyst with dual-center active sites is finally obtained, labeled as MnO2 / Fe2O3-Al2O3-SiO2.

[0110] The prepared heterogeneous ozone catalyst contained 7.0 wt% MnO2, 6.7 wt% Fe2O3, 10.7 wt% SiO2, and 75.6 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.27 g / mL, and the average particle strength was 159 N / particle.

[0111] The obtained heterogeneous ozone catalyst (MnO2 / Fe2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 70% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4.5, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the stable TOC of the effluent was measured to be 35.2 ppm (the change of effluent TOC with operating time is shown in Figure 4). The mineralization efficiency of organic pollutants reached 58.4%.

[0112] Results Analysis: Compared with Example 5, the ozone catalyst in Example 4 showed significantly better catalytic effect in the ozone oxidation degradation of organic matter in wastewater. This is because the active sites of iron oxide can serve as loading sites for transition metal oxides, and the two are bonded together through metal-oxygen bonds. Therefore, when the content of transition metal oxides is too high, it will excessively cover the iron oxide exposed on the inner surface of the pores, which will cause a decrease in the catalytic activity of the heterogeneous ozone catalyst.

[0113] Comparative Example 1

[0114] The only difference between this comparative example and Example 1 is that: the cobalt acetate aqueous solution impregnation is not performed, i.e., step S4 is not performed, and the second transition metal oxide precursor is not loaded on the inner surface of the catalyst channels; otherwise, it is consistent with Example 1. Finally, an ozone catalyst containing a single central active site in the matrix was obtained, labeled as Fe2O3-Al2O3-SiO2, and its optical microscope image is shown in Figure 2(A), and its XRD pattern is shown in Figure 3.

[0115] The prepared ozone catalyst contained 5.0 wt% Fe2O3, 12.4 wt% SiO2, and 82.6 wt% Al2O3. The heterogeneous ozone catalyst had a particle bulk density of 1.26 g / mL and an average particle strength of 161 N / particle.

[0116] The obtained ozone catalyst (Fe2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 50% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4, the water treatment rate was 500 ml per hour, and the system operated stably for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the TOC of the stable effluent was measured to be 50.3 ppm (the change of effluent TOC with operating time is shown in Figure 4). The mineralization efficiency of organic pollutants reached 40.47%.

[0117] Results Analysis: Compared with Comparative Example 1, the ozone catalyst in Example 1 showed significantly better catalytic oxidation and degradation of organic matter in wastewater. This is because the iron oxide in the catalyst matrix exists in the form of highly aggregated micro-nano particles. Therefore, when the catalyst uses a single active center distributed within the matrix, its ability to catalyze the oxidation of ozone to form active free radicals is relatively low.

[0118] Comparative Example 2

[0119] The only difference between this comparative example and Example 2 is that the catalyst matrix does not contain iron oxide, i.e., iron hydroxide powder is not added in step S1; the rest of the operation is consistent with Example 2. The final ozone catalyst with a single central active site on the inner surface of the pores is labeled CuO / Al2O3-SiO2.

[0120] The prepared ozone catalyst contained 3.0 wt% CuO, 15.0 wt% SiO2, and 82.0 wt% Al2O3. The heterogeneous ozone catalyst had a particle bulk density of 1.27 g / mL and an average particle strength of 170 N / particle.

[0121] The obtained ozone catalyst (CuO / Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 50% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4, the water treatment rate was 500 ml per hour, and the system operated stably for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the TOC of the stable effluent was measured to be 45.8 ppm (the change of effluent TOC with operating time is shown in Figure 4). The mineralization efficiency of organic pollutants reached 45.79%.

[0122] Results Analysis: Compared with Comparative Example 2, the ozone catalyst in Example 2 showed significantly better catalytic ozone oxidation degradation of organic matter in wastewater. This is because, when used for wastewater treatment, the CuO loaded on the inner surface of the catalyst pores is easily lost with the water flow, resulting in a decrease in catalytic activity. Therefore, when the catalyst uses a single active center distributed on the inner surface of the pores, the catalytic activity is low.

[0123] Comparative Example 3

[0124] The only difference between this comparative example and Example 1 is that the iron oxide in the catalyst matrix is ​​replaced with an equimolar amount of Co2O3, that is, in step S1, 16 grams of iron hydroxide powder is replaced with 12.4 grams of Co2O3 powder; the rest of the operation is the same as in Example 1. The final ozone catalyst obtained has Co2O3 as the central active site on both the inner surface of the pores and in the matrix, labeled as Co2O3 / Co2O3-Al2O3-SiO2.

[0125] The prepared heterogeneous ozone catalyst contained 6.1 wt% Co2O3, 12.4 wt% SiO2, and 81.5 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.27 g / mL, and the average particle strength was 159 N / particle.

[0126] The obtained heterogeneous ozone catalyst (Co2O3 / Co2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 50% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the TOC of the stable effluent was measured to be 38.9 ppm, and the mineralization efficiency of organic pollutants reached 54%.

[0127] Comparative Example 4

[0128] The only difference between this comparative example and Example 1 is that the Co2O3 loaded on the inner surface of the catalyst channels is replaced with an equimolar amount of iron oxide, i.e., the cobalt acetate aqueous solution is replaced with an iron acetate aqueous solution in step S4; the rest of the operation is consistent with Example 1. The final ozone catalyst obtained has Fe2O3 as the central active site on both the inner surface of the channels and in the matrix, labeled as Fe2O3 / Fe2O3-Al2O3-SiO2.

[0129] The prepared heterogeneous ozone catalyst contained 7.1 wt% Fe2O3, 12.4 wt% SiO2, and 80.5 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.28 g / mL, and the average particle strength was 159 N / particle.

[0130] The obtained heterogeneous ozone catalyst (Fe2O3 / Fe2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 50% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the TOC of the stable effluent was measured to be 39.2 ppm, and the mineralization efficiency of organic pollutants reached 53.6%.

[0131] Comparative Example 5

[0132] The only difference between this comparative example and Example 1 is that the iron oxide in the catalyst matrix is ​​replaced with an equimolar amount of Co2O3, and the Co2O3 loaded on the inner surface of the catalyst channels is replaced with an equimolar amount of iron oxide. Specifically, in step S1, 16 grams of iron hydroxide powder is replaced with 12.4 grams of Co2O3 powder, and in step S4, the cobalt acetate aqueous solution is replaced with an iron acetate aqueous solution. The remaining operations are consistent with Example 1. The resulting ozone catalyst, labeled Fe2O3 / Co2O3-Al2O3-SiO2, has Fe2O3 and Co2O3 as the central active sites on the inner surface of the channels and in the matrix, respectively.

[0133] The prepared heterogeneous ozone catalyst contained 3.9 wt% Co2O3, 2.8 wt% Fe2O3, 12.4 wt% SiO2, and 80.9 wt% Al2O3. The particle bulk density of the heterogeneous ozone catalyst was 1.29 g / mL, and the average particle strength was 160 N / particle.

[0134] The obtained heterogeneous ozone catalyst (Fe2O3 / Co2O3-Al2O3-SiO2) was filled into the water treatment device for continuous catalytic oxidation of actual coal chemical wastewater. The hydraulic contact time between the wastewater and the catalyst was 30 minutes, the catalyst occupied 50% of the effective volume of the reactor, the ratio of ozone dosage to the organic matter removal concentration (ΔTOC) in the water was 4, the water treatment rate was 500 ml per hour, and the continuous stable operation lasted for 6.0 hours. The TOC of the influent was 84.5 ppm. After 4 hours of continuous influent and effluent operation, the TOC of the stable effluent was measured to be 40.4 ppm, and the mineralization efficiency of organic pollutants reached 52.1%.

[0135] Results Analysis: Compared with Comparative Examples 3-5, the ozone catalysts in Examples 1-4 showed significantly better catalytic effects in the ozone oxidation and degradation of organic matter in wastewater. This indicates that in heterogeneous ozone catalysts, the metal oxides used for the two active centers affect the synergistic effect between them, thus influencing the catalytic activity. This invention, by using iron oxide as the active center dispersed in the matrix and cobalt oxide, manganese oxide, nickel oxide, or copper oxide as the active center supported on the inner surface of the pores, enables better synergistic effects between the two active centers, resulting in higher catalytic activity for the heterogeneous ozone catalyst.

[0136] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0137] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a heterogeneous ozone catalyst with dual-center active sites, characterized in that, include: (1) Mix the catalyst matrix raw materials, including iron oxide source, and add adhesive to knead to obtain a premix; (2) Shape, dry and calcine the premix to obtain a catalyst matrix containing iron oxide; (3) Place the catalyst matrix in a cobalt salt solution, fully impregnate it, dry it, and then calcine it to convert the cobalt salt into cobalt oxide to obtain a multiphase ozone catalyst, which includes a catalyst matrix with a porous structure, iron oxide dispersed in the catalyst matrix, and cobalt oxide loaded on the inner surface of the pores in the catalyst matrix.

2. The preparation method according to claim 1, characterized in that, In the multiphase ozone catalyst, the contents of iron oxide and cobalt oxide are 5.0~10.0 wt% and 2.2~3.8 wt%, respectively.

3. The preparation method according to claim 1 or 2, characterized in that, The catalyst matrix comprises iron oxide, silicon dioxide, and aluminum oxide.

4. The preparation method according to claim 1, characterized in that, In step (1), the iron oxide source is iron oxide and / or iron hydroxide, and its content in the catalyst matrix raw material is 3.5~15 wt%.

5. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the cobalt salt solution is 0.05~0.50 mol / L, the mass-to-volume ratio between the catalyst matrix and the cobalt salt solution is 1.0 g: 1.2~2.0 mL, and the time for full impregnation is 10~15 h.

6. The preparation method according to claim 1 or 4, characterized in that, In step (1), the catalyst matrix raw material includes the following components in parts by weight: 120-180 parts of activated alumina, 77-120 parts of boehmite, 25-45 parts of glass fiber, 16-35 parts of iron oxide source, and 7-11 parts of pore-forming agent.

7. The preparation method according to claim 1, characterized in that, In step (2), the roasting is carried out in an aerobic atmosphere at a temperature of 450~500℃ for 3.5~4.5 h; in step (3), the roasting is carried out in an aerobic atmosphere at a temperature of 400~450℃ for 3~6 h.

8. The application of the heterogeneous ozone catalyst prepared by the preparation method according to any one of claims 1 to 7 in the catalytic ozone oxidation degradation of organic matter.

9. The application of the heterogeneous ozone catalyst prepared by any one of the preparation methods described in claims 1 to 7 in the treatment of organic polluted wastewater.

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