In-situ surface modified perovskite type catalyst as well as preparation method and application thereof

Abstract

The invention relates to an in-situ surface modified perovskite type catalyst and a preparation method and application thereof.The preparation method comprises the steps that firstly, a perovskite type catalyst with the chemical general formula being AxByCozOv and without in-situ surface modification is prepared, the catalyst is subjected to in-situ treatment with ozone, the surface structure of perovskite is changed through the treatment, and then the perovskite type catalyst with the in-situ surface modification function is obtained; the in-situ surface modified perovskite type catalyst A < x > B < y > Co < z > O < v-O > is formed; the catalyst has higher catalytic activity and stability. The in-situ surface modified perovskite type catalyst can be used for ozone room-temperature catalytic decomposition and VOC room-temperature catalytic ozonation reaction, and has an excellent catalytic effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to an in-situ surface-modified perovskite catalyst and a preparation method and application thereof. Background Art

[0002] Ozone (O3) is a ubiquitous pollutant present near the ground and in commercial aviation worldwide, significantly harming ecosystems and human health. Even long-term exposure to low concentrations of ozone can cause symptoms or illnesses, including cardiovascular, blood pressure, respiratory, and lung function impairments. Therefore, effective ozone removal methods are urgently needed, both at the source and through indoor purification, to protect public health and safety.

[0003] Ozone, as a strong oxidant, it is feasible to use ozone as an oxidant to eliminate pollutants. Ozone oxidation technology has been used very early, and some sewage treatment plants use the strong oxidizing properties of ozone to sterilize and disinfect sewage. Today, ozone oxidation technology is still widely used in the fields of disinfection of daily necessities, degradation of industrial VOCs, and sewage treatment. However, the efficiency of ozone oxidation of VOCs is low, so the ozone concentration used by most manufacturers is extremely high, which is the national secondary standard (160μg / m 3 , GB 3095-2012) 100,000 to 1 million times, causing extremely serious ozone secondary pollution. Therefore, efficient use of ozone oxidation, improve green product selectivity, eliminate secondary pollution, and reduce energy consumption.

[0004] Perovskites are a class of metal oxides composed of transition metals and rare earth or alkaline earth metals. They have been shown to exhibit both good catalytic activity and high stability. Due to their variability in composition and structure, perovskite-type metal oxides exhibit diverse physicochemical properties (such as redox behavior, oxygen mobility, and electronic and ionic conductivity). Over the past few decades, they have been extensively studied and applied in various fields.

[0005] In current research, patent publication number CN107376926A discloses a LaFeO3 perovskite-type ozone catalyst prepared via a citric acid sol-gel method. While achieving nearly 100% ozone conversion at room temperature and in a dry environment, the conversion rate is less than 90% at 90% humidity, making it impractical for practical application. Patent CN114210338A discloses a perovskite-like catalyst for catalytic ozone oxidation. The catalyst boasts stable chemical properties, reusability, high catalytic activity, environmental friendliness, and no water pollution. However, the catalyst's hydrothermal-calcination preparation method is complex and cumbersome, requiring high reaction conditions, hindering its mass production and widespread application. In recent years, various synthetic perovskite metal oxides have been reported to improve their physicochemical properties and catalytic activity through methods such as metal or non-metallic element doping, acid treatment, alkali treatment, and H2O2 treatment. Patent CN117943045A discloses a method for preparing and applying a composite material enriched with oxygen vacancies by simultaneously manipulating the A and B sites of LaMnO3 materials. The catalyst uses a sol-gel method to replace part of the Mn at the B position with Cu to obtain La2CuMnO6-n, and then uses nitric acid to soak and etch part of the La element at the A position, converting part of the La2CuMnO6-n into MnO2, thereby successfully preparing the required composite material. The prepared composite material has oxygen-rich vacancies and can be used in high-humidity environments to efficiently and stably catalyze the long-term ozone degradation of organic pollutants in exhaust gas. However, the modification process of acid etching and water washing is complicated, and the minimum VOC degradation temperature is 35°C. The VOC conversion rate and CO2 selectivity do not reach 50%. Although this catalyst can degrade pollutants by catalyzing ozone oxidation, the operating temperature is too high, the energy-saving effect is not obvious, and there is a risk of secondary pollution.

[0006] These existing preparation methods and modification processes are complex, and their performance is poor under conditions of high humidity and high air volume. They have defects such as difficulty in industrialization, low efficiency, difficulty in regeneration, and easy moisture absorption. The market is currently in urgent need of a catalyst that can achieve in-situ surface modification through ozone, can efficiently degrade ozone at room temperature, and use ozone to catalyze the ozonation of pollutants. The catalyst is low-priced, can be industrially mass-produced, and can meet the requirements of room temperature and even high humidity environments. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides an in-situ surface-modified perovskite catalyst and a preparation method and application thereof.

[0008] The technical solution adopted by the present invention is: a method for preparing an in-situ surface-modified perovskite catalyst, first synthesizing a general formula A x B y Co z O vThe perovskite material with the general formula A x B y Co z O v The perovskite material was placed in an ozone environment for in-situ surface modification to obtain A x B y Co z O v -O;

[0009] A is one or more rare earth metal elements or alkaline earth metal elements, B is one or more first transition series metal elements excluding cobalt, 0<x≤10, 0≤y≤10, 0<z≤10, 0<v≤30.

[0010] Preferably, A is one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Be, Mg, Ca, Sr, Ba and Ra;

[0011] B is one or more of Ti, V, Cr, Mn, Fe, Ni, Cu and Zn.

[0012] Preferably, A includes Sr; and B includes Mn.

[0013] Preferably, the steps are as follows:

[0014] Step 1: adding one or more of the A-site metal salts, one or more of the B-site metal salts, and a cobalt salt into deionized water to dissolve into a metal salt solution;

[0015] Step 2: dissolving an organic complexing agent in a metal salt solution, heating and stirring until the mixture becomes gel-like; the molar ratio of the organic complexing agent to the metal salt in the metal salt solution is 1:0.2-5;

[0016] Step 3: Dry the gel and calcine it in an oxygen-containing environment at 400-1000°C for 1-24 hours to obtain the perovskite catalyst A without in-situ modification. x B y Co z O v ;

[0017] Step 4: A x B y Co z O v Place in an environment with relative humidity RH=20-95% humidity and ozone concentration of 10-1000ppm for in-situ modification for 0.1-10h to obtain A x B y Co z O v -O.

[0018] Preferably, in step 1, the anion form of the A-site metal salt, the B-site metal salt and the cobalt salt includes NO 3- 、Cl - 、SO3 2- 、SO4 2- OH - 、SiO3 2- PO4 3- 、CH3COO - 、CO3 2- 、HCO3 - 、C2O4 2- One or more of.

[0019] Preferably, the organic complexing agent is one or more of ethylenediaminetetraacetic acid, ascorbic acid, citric acid, ketoxime, hydroxymethyl urea, dimethyl sulfoxide, diethyl dithiocarbamate, ethanedinitrile, ethylene glycol dimethyl phosphonic acid, ethylene glycol diisopropyl phosphonic acid, ethylene glycol diethyl phosphonic acid, tri(methyl)phosphonic acid hydroxide, tri(isopropyl)phosphonic acid hydroxide and tri(ethyl)phosphonic acid hydroxide.

[0020] Preferably, in step 2, the mixture is stirred at a speed of 300 to 500 rpm and a temperature of 70 to 95° C. until the deionized water in the solution is evaporated to form a gel.

[0021] Preferably, in step 4, the in-situ modification is carried out for 0.5 to 2 hours at a relative humidity of RH = 50 to 95% and an ozone concentration of 100 to 400 ppm to obtain A x B y Co z O v -O.

[0022] The invention relates to an in-situ surface modified perovskite catalyst prepared by a preparation method of the in-situ surface modified perovskite catalyst.

[0023] Preferably, SrCoO 3–δ -O, SrMn 0.4 Co 0.6 O 3–δ -O, SrMn 0.6 Co 0.4 O 3–δ -O、SrFe 0.2 Co 0.8 O 3–δ -O、Sr 0.9 Ce 0.1 CoO 3–δ -O、Sr 0.5 Ba 0.5 CoO 3–δ -O and Sr 0.9 Ce 0.1Mn 0.5 Co 0.5 O 3–δ -O, 0<δ≤0.5.

[0024] Application of in situ surface-modified perovskite catalysts in room-temperature catalytic decomposition of ozone or room-temperature catalytic ozonation of VOCs

[0025] The advantages and positive effects of the present invention are: providing an in-situ surface-modified perovskite catalyst with high catalytic activity and stability, optimizing the perovskite surface structure through in-situ ozone treatment of the surface, and forming a new catalyst with high catalytic ability and stability;

[0026] The in-situ surface-modified perovskite catalyst is a catalyst that uses rare earth metal or alkaline earth metal oxides, transition metals, and cobalt metal oxides to work together. Ozone in-situ treatment allows these elements to work together, resulting in extremely strong catalytic activity.

[0027] The initial perovskite catalyst is prepared using the sol-gel method, which has the advantages of simple operation and short time consumption. The in-situ surface-modified perovskite catalyst has a simple modification process, low raw material cost, and an environmentally friendly preparation method. The new catalyst is also highly stable and has a long service life, making it easy to industrialize.

[0028] In situ surface-modified perovskite catalysts have significant effects on ozone decomposition and VOCs catalytic ozonation, especially in the currently challenging room temperature, high concentration, and high humidity environments, and have excellent catalytic effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD pattern of the perovskite catalyst SrCoO3-δ (0<δ≤0.5) without in-situ modification;

[0030] Figure 2 SEM image of the perovskite catalyst SrCoO3-δ (0<δ≤0.5) without in-situ modification;

[0031] Figure 3 BET adsorption-desorption curves of the perovskite catalyst SrCoO3-δ (0<δ≤0.5) without in-situ modification;

[0032] Figure 4 XRD pattern of in-situ modified perovskite catalyst SrCoO3-δ-O (0<δ≤0.5);

[0033] Figure 5 SEM image of the in-situ modified perovskite catalyst SrCoO3-δ-O (0<δ≤0.5);

[0034] Figure 6BET adsorption-desorption curves of in-situ modified perovskite catalyst SrCoO3-δ-O (0<δ≤0.5);

[0035] Figure 7 Example 1 Catalytic stability study of catalyst;

[0036] Figure 8 Changes in VOC gas concentration in the control group;

[0037] Figure 9 Example 1: Conversion efficiency of the catalyst in VOC ozonation. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0039] The present invention relates to an in-situ surface modified perovskite catalyst and its preparation method and application. First, a catalyst having a chemical formula A is prepared. x B y Co z O v The perovskite catalyst without in-situ surface modification was treated in-situ with ozone, which changed the surface structure of the perovskite to form an in-situ surface modified perovskite catalyst A. x B y Co z O v -O; This catalyst has higher catalytic activity and stability. Catalyst A x B y Co z O v or A x B y Co z O v In the general formula of -O, A is any one or more rare earth metal elements or alkaline earth metal elements, B is any one or more first transition series transition metal elements that do not contain cobalt, 0 < x ≤ 10, 0 ≤ y ≤ 10, 0 < z ≤ 10, and 0 < v ≤ 30. x is 0.1, 0.5, 0.3, 1, 1.2, or 6; y is 0.1, 0.2, 0.5, 1, 2, 3, or 5; z is 0.1, 0.2, 0.5, 1, 2, 3, or 5; and v is 2.5, 3, 5, 6.3, 10, 15, 20, or 25.

[0040] Specifically, A is selected from any one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Be, Mg, Ca, Sr, Ba, and Ra, and preferably A is selected from any one or more of La, Ce, Ca, Sr, and Ba. In certain embodiments of the present invention, A must contain the element Sr, which is easily enriched on the surface of Sr and interacts more significantly with transition metal elements and cobalt elements, so that the ozone in-situ treatment synergistically changes the surface structure of the perovskite, thereby improving the catalytic activity.

[0041] B is selected from any one or more of Ti, V, Cr, Mn, Fe, Ni, Cu, and Zn, and preferably B is selected from any one or more of Ti, Mn, Fe, Ni, and Cu. In certain embodiments of the present invention, B must contain Mn, as the interaction between Mn and cobalt is more pronounced, resulting in a more significant improvement in catalytic efficiency.

[0042] The preparation method of the in-situ surface-modified perovskite catalyst comprises the following steps:

[0043] Step 1: adding one or more of the metal salts at position A, one or more of the metal salts at position B and a cobalt salt into deionized water to dissolve into a metal salt solution; the anion forms of the metal salts at position A, the metal salts at position B and the cobalt salt include NO 3- 、Cl - 、SO3 2- 、SO4 2- OH - 、SiO3 2- PO4 3- 、CH3COO - 、CO3 2- 、HCO3 - 、C2O4 2- One or more, more preferably NO3 - 、Cl - 、CH3COO - , one or more;

[0044] Step 2: dissolving an organic complexing agent in the metal salt solution in step 1, and transferring the solution to a heated magnetic stirrer for uniform stirring until a gel is obtained; the organic complexing agent is at least one of ethylenediaminetetraacetic acid, ascorbic acid, citric acid, ketoxime, hydroxymethylurea, dimethyl sulfoxide, diethyl dithiocarbamate, ethanedinitrile, ethylene glycol dimethyl phosphate, ethylene glycol diisopropyl phosphate, ethylene glycol diethyl phosphate, tri(methyl)phosphoric acid hydroxide, tri(isopropyl)phosphoric acid hydroxide, and tri(ethyl)phosphoric acid hydroxide, and more preferably at least one of ethylenediaminetetraacetic acid, ascorbic acid, and citric acid; and the dissolution process is stirring at a speed of 300-400 rpm for 20-30 minutes until completely dissolved. Stirring can fully complex the metal ions free in the deionized water with the organic complexing agent; the heating process is to stir at a speed of 300 to 500 rpm and a temperature of 70 to 95° C. until the deionized water in the solution is evaporated to form a gel; the molar ratio of the organic complexing agent to the metal salt in the metal salt solution is 1:0.2 to 5, preferably 1:0.5 to 2;

[0045] Step 3: Transfer the gel obtained in step 2 to an oven for drying, and then transfer it to a muffle furnace for high-temperature calcination to obtain a perovskite catalyst A that has not been in situ modified. x B y Co z O v ; calcining in an oxygen-containing environment, the calcination temperature is 400 to 1000 ° C, preferably 500 to 900 ° C, the calcination time is 1 to 24 hours, preferably 1 to 10 hours, more preferably 1 to 8 hours; the oxygen-containing environment is an air atmosphere or an oxygen atmosphere;

[0046] Step 4: Place the perovskite catalyst prepared in step 3 into a sample tube and perform in-situ modification for 0.1 to 10 hours in an environment with a relative humidity of RH = 20 to 95% and an ozone concentration of 10 to 1000 ppm to obtain a surface-modified perovskite catalyst A. x B y Co z O v -O; preferably, the in-situ modification is carried out for 0.5 to 2 hours at a relative humidity RH = 50 to 95% humidity and an ozone concentration of 100 to 400 ppm.

[0047] In-situ surface modified perovskite catalysts are metal oxides composited with transition metals, rare earths and alkaline earth metals, with a microscopic morphology of nanoparticles. Through appropriate element ratios and experimental conditions, nanoparticles of 10nm to 1μm can be obtained. The specific surface area of ​​in-situ surface modified perovskite catalysts is 1-20m 2 / g, and the surface has a large number of catalytic active sites.

[0048] Under appropriate conditions, the addition of transition metal elements enables the catalyst to regulate the catalytic active sites of Co-O, resulting in the weakening of the interaction between Co and external O*, thereby improving the efficiency of ozone decomposition and greatly improving the catalytic activity of the catalyst. Cobalt metal itself can also achieve ozone decomposition and VOC catalytic ozonation through its rich valence states and valence change capabilities. In addition, the electron transfer between different valence states of transition metal elements and between transition metal elements and cobalt elements provides more possibilities for the decomposition of ozone on the catalyst. This catalytic material can have a good catalytic effect in room temperature, high and low humidity, high and low air volume, and high and low concentration environments.

[0049] In situ surface-modified perovskite catalysts can be used for room-temperature catalytic decomposition of ozone and ozonation of VOCs, offering advantages such as high stability and a long service life. The in situ surface-modified perovskite catalysts do not contain precious metals, resulting in low cost. Furthermore, the material's preparation method is relatively mature, and the modification process is simple, making it suitable for mass production and widespread adoption. The application of these in situ surface-modified perovskite catalysts in ozone purification and VOC degradation can effectively degrade ozone and other pollutants, reducing air pollution concentrations.

[0050] In situ surface-modified perovskite catalysts can be used for catalytic ozone decomposition and VOC ozonation. Placing the in situ surface-modified perovskite catalyst in an ozone environment allows for ozone decomposition through its catalytic action. Alternatively, placing the in situ surface-modified perovskite catalyst in an environment containing VOCs and introducing ozone allows for catalytic ozonation of the VOCs, effectively removing VOCs. The catalyst also effectively degrades ozone, effectively controlling the ozone content in exhaust gas.

[0051] The in-situ surface-modified perovskite catalyst has a significant effect on the catalytic decomposition of ozone and the catalytic ozonation of VOCs. It not only has efficient catalytic ability in room temperature environments, but can also produce equally excellent catalytic effects in the currently difficult high-concentration, high-humidity environments. The catalyst can function in a variety of scenarios such as high humidity, high air volume, and high ozone concentration, and has excellent ozone and VOC purification effects and industrial application potential. Compared with unmodified perovskite catalysts, in-situ surface-modified perovskite catalysts only require lower reaction temperatures and energy consumption in the catalytic decomposition of ozone, allowing ozone and VOC pollutants to be efficiently treated and purified, which plays an extremely important role in pollution control in different industries, protection of the atmospheric environment, and protection of people's lives, health and safety.

[0052] When the in-situ surface-modified perovskite catalyst is used for ozone and VOC catalytic purification, the powder of the in-situ surface-modified perovskite catalyst can be granulated and put into use in the equipment. In order to reduce the catalytic cost and minimize the loss of the catalyst due to gas purging during the treatment process, it is preferred to mix the in-situ surface-modified perovskite catalyst with a carrier to form a composite catalyst. For example, the solution and / or slurry of the in-situ surface-modified perovskite catalyst is coated on a carrier such as a carbon material, a ceramic material, a foam material or a solid acid material to be immobilized on the carrier. On the one hand, it is beneficial for the passage of the gas to be treated and its contact with the catalyst. On the other hand, it reduces the loss of the catalyst, extends the service life of the catalyst, and reduces the cost of using the catalyst. At the same time, it can also increase the specific surface area of ​​the overall composite catalyst after loading, thereby further improving the catalytic efficiency.

[0053] The carrier can be a composite of one or more of ZrO2, TiO2, SiO2, WO3, Nb2O5, SnO2, Al2O3, Co3O4, CeO2, Fe2O3, activated carbon, graphene, clay, zeolite, metal-organic framework, covalent organic framework, honeycomb ceramic, foam ceramic, metal ceramic, foam, sponge, polyurethane cotton, and non-woven fabric. In addition to the above carriers, any carrier currently used in ozone treatment catalysts is also applicable.

[0054] In situ surface modified perovskite catalyst A x B y Co z O v When -O is used for catalytic decomposition of ozone or VOC, the gas flow is brought into contact with the catalyst in a temperature range of -40°C to 500°C, and decomposition is achieved under the catalytic action. The temperature is preferably in the range of 0°C to 100°C, and more preferably in the range of 10°C to 50°C.

[0055] When the in-situ surface-modified perovskite catalyst is used for ozone and VOC catalytic purification, its catalytic conditions, process flow, etc. are compatible with the catalytic conditions and process flow of the existing technology. For example, the in-situ surface-modified perovskite catalyst of this application can be used to replace the existing catalyst, and other process parameters and equipment can maintain the original data.

[0056] The present invention is described below with reference to the accompanying drawings. Experimental methods without specific operating steps are carried out in accordance with the corresponding product specifications. Unless otherwise specified, the instruments, reagents, and consumables used in the examples can be purchased from commercial companies.

[0057] Example 1: Preparation of in-situ surface-modified perovskite catalyst

[0058] Preparation of in situ surface-modified perovskite catalyst SrCoO 3-δ-O(0<δ≤0.5), including the following steps:

[0059] (1) Add 1 mmol of strontium nitrate and 1 mmol of cobalt nitrate to 50 ml of deionized water and stir at 300 rpm for 30 min;

[0060] (2) dissolving 2 mmol of citric acid in the solution of step (1), transferring the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 80°C and stirring at 400 rpm until it forms a gel;

[0061] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at 180°C for 2 hours; and then transferred to a muffle furnace for high-temperature calcination at 800°C for 4 hours to obtain a perovskite-type catalyst SrCoO that was not in situ modified. 3-δ (0<δ≤0.5).

[0062] Perovskite-type catalyst SrCoO without in situ modification 3-δ (0<δ≤0.5), XRD test results are as follows Figure 1 As shown, it can be seen that its main phase is Sr6Co5O 15 The crystal structure of the SEM test results are as follows Figure 2 As shown in the figure, it can be seen that its morphology is nanoparticles, and the particle size of micro nanoparticles is between 400nm-1μm. The BET test results are as follows Figure 3 As shown, the specific surface area is 1.96m 2 / g; the BET adsorption-desorption curve is a typical type IV isotherm, indicating that it has a mesoporous structure, and the distribution of the mesoporous structure is conducive to the occurrence of various reactions.

[0063] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube and in situ modified for 1 hour in an environment with a relative humidity of RH = 90% and an ozone concentration of 100 ppm to obtain a surface-modified perovskite catalyst SrCoO 3-δ -O(0<δ≤0.5).

[0064] The in situ surface-modified perovskite catalyst SrCoO 3-δ -O (0 < δ ≤ 0.5) was characterized, and the XRD test results were as follows Figure 4 As shown, it shows that its main phase is Sr6Co5O 15 The crystal structure of the surface of the product is different from that of SrCO3 and SrCoO3. The SEM test results are as follows: Figure 5 As shown in the figure, the morphology is nanoparticle-like, and the particle size of the microscopic nanoparticles is still between 400nm-1μm, but the surface becomes rough. The BET test results are as follows Figure 6As shown, the specific surface area is 3.70m 2 / g; the BET adsorption-desorption curve is a typical type IV isotherm, indicating that it has a mesoporous structure, and the distribution of the mesoporous structure is conducive to the occurrence of various reactions.

[0065] Example 2

[0066] Preparation of in situ surface-modified perovskite catalyst SrMn 0.4 Co 0.6 O 3-δ -O(0<δ≤0.5), including the following steps:

[0067] (1) Add 1 mmol of strontium nitrate, 0.4 mmol of manganese nitrate, and 0.6 mmol of cobalt nitrate to 50 ml of deionized water and stir at 400 rpm for 20 min;

[0068] (2) dissolving 3 mmol of citric acid in the solution of step (1), transferring the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 80°C and stirring at 300 rpm until it forms a gel;

[0069] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at a temperature of 120°C for 4 hours; and then transferred to a muffle furnace for high-temperature calcination at a temperature of 900°C for 4 hours to obtain a perovskite catalyst SrMn that was not in situ modified. 0.4 Co 0.6 O 3-δ (0<δ≤0.5);

[0070] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube and in situ modified for 1 hour in an environment with a relative humidity of RH = 80% and an ozone concentration of 400 ppm to obtain a surface-modified perovskite catalyst SrMn 0.4 Co 0.6 O 3-δ -O(0<δ≤0.5).

[0071] Example 3

[0072] Preparation of in situ surface-modified perovskite catalyst SrMn 0.6 Co 0.4 O 3-δ -O(0<δ≤0.5), including the following steps:

[0073] (1) Add 1 mmol of strontium nitrate, 0.6 mmol of manganese nitrate, and 0.4 mmol of cobalt nitrate to 100 ml of deionized water and stir at 350 rpm for 25 min;

[0074] (2) dissolving 2 mmol of citric acid and 1 mmol of ethylenediaminetetraacetic acid into the solution in step (1), transferring the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 90°C and stirring at 300 rpm until it forms a gel;

[0075] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at 120°C for 4 hours; and then transferred to a muffle furnace for high-temperature calcination at 900°C for 3 hours to obtain a perovskite catalyst SrMn that was not in situ modified. 0.6 Co 0.4 O 3-δ (0<δ≤0.5);

[0076] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube in an environment with a relative humidity of RH = 95% and an ozone concentration of 50 ppm for in-situ modification for 1.5 h to obtain a surface-modified perovskite catalyst SrMn 0.6 Co 0.4 O 3-δ -O(0<δ≤0.5).

[0077] Example 4

[0078] Preparation of in situ surface-modified perovskite catalyst SrFe 0.2 Co 0.8 O 3-δ -O(0<δ≤0.5), including the following steps:

[0079] (1) Add 1 mmol of strontium nitrate, 0.2 mmol of iron nitrate, and 0.8 mmol of cobalt nitrate to 50 ml of deionized water and stir at 400 rpm for 30 min;

[0080] (2) dissolving 2 mmol of citric acid in the solution of step (1), transferring the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 80°C and stirring at 400 rpm until it forms a gel;

[0081] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at a temperature of 180°C for 2 hours; and then transferred to a muffle furnace for high-temperature calcination at a temperature of 800°C for 4 hours to obtain a perovskite catalyst SrFe 0.2 Co 0.8 O 3-δ (0<δ≤0.5);

[0082] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube in an environment with a relative humidity of RH = 90% and an ozone concentration of 100 ppm for in-situ modification for 1 hour to obtain a surface-modified perovskite catalyst SrFe 0.2 Co 0.8 O 3-δ -O(0<δ≤0.5).

[0083] Example 5

[0084] Preparation of in situ surface-modified perovskite catalyst SrMn 0.6 Co 0.4 O 3-δ -O(0<δ≤0.5), including the following steps:

[0085] (1) Add 0.9 mmol of strontium nitrate, 0.1 mmol of cerium nitrate, and 1 mmol of cobalt nitrate to 100 ml of deionized water and stir at 300 rpm for 30 min;

[0086] (2) Dissolve 2 mmol of citric acid in the solution of step (1), transfer the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 90°C and stir at 300 rpm until it forms a gel;

[0087] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at a temperature of 120° C. for 4 h; and then transferred to a muffle furnace for high-temperature calcination at a temperature of 900° C. for 3 h to obtain a perovskite catalyst Sr that was not in situ modified. 0.9 Ce 0.1 CoO 3-δ (0<δ≤0.5);

[0088] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube and in situ modified for 5 h in an environment with a relative humidity of RH = 50% and an ozone concentration of 1000 ppm to obtain a surface-modified perovskite catalyst SrMn 0.6 Co 0.4 O 3-δ -O(0<δ≤0.5).

[0089] Example 6

[0090] Preparation of in situ surface-modified perovskite catalyst Sr 0.5 Ba 0.5 CoO 3-δ -O(0<δ≤0.5), including the following steps:

[0091] (1) Add 0.5 mmol of strontium nitrate, 0.5 mmol of barium nitrate, and 1 mmol of cobalt nitrate to 100 ml of deionized water and stir at 350 rpm for 30 min;

[0092] (2) Dissolve 2 mmol of citric acid in the solution of step (1), transfer the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 90°C and stir at 350 rpm until it forms a gel;

[0093] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at 120°C for 2 hours; and then transferred to a muffle furnace for high-temperature calcination at 900°C for 1 hour to obtain a perovskite catalyst Sr that was not in situ modified. 0.5 Ba 0.5 CoO 3-δ (0<δ≤0.5);

[0094] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube and in situ modified for 2 h in an environment with a relative humidity of RH = 75% and an ozone concentration of 1000 ppm to obtain a surface-modified perovskite catalyst Sr 0.5 Ba 0.5 CoO 3-δ -O(0<δ≤0.5).

[0095] Example 7

[0096] Preparation of in situ surface-modified perovskite catalyst Sr 0.9 Ce 0.1 Mn 0.5 Co 0.5 O 3-δ -O(0<δ≤0.5), including the following steps:

[0097] (1) Add 0.9 mmol of strontium nitrate, 0.1 mmol of cerium nitrate, 0.5 mmol of manganese nitrate, and 0.5 mmol of cobalt nitrate to 100 ml of deionized water and stir at 300 rpm for 30 min;

[0098] (2) dissolving 1 mmol of citric acid and 1 mmol of ethylenediaminetetraacetic acid into the solution in step (1), transferring the mixed solution obtained by thorough stirring to a heated magnetic stirrer at 90°C and stirring at 400 rpm until it forms a gel;

[0099] (3) The gel obtained in step (2) was transferred to an oven for heating and drying at 120°C for 2 hours; and then transferred to a muffle furnace for high-temperature calcination at 900°C for 1 hour to obtain a perovskite catalyst Sr that was not in situ modified.0.9 Ce 0.1 Mn 0.5 Co 0.5 O 3-δ (0<δ≤0.5);

[0100] (4) The perovskite catalyst prepared in step (3) was placed in a sample tube and in situ modified for 0.5 h in an environment with a relative humidity of RH = 95% and an ozone concentration of 100 ppm to obtain a surface-modified perovskite catalyst Sr 0.9 Ce 0.1 Mn 0.5 Co 0.5 O 3-δ -O(0<δ≤0.5).

[0101] Comparative Example 1

[0102] Preparation of in situ surface-modified perovskite catalyst SrCoO 3-δ -O(1100°C)(0<δ≤0.5), used for room temperature ozone decomposition reaction, the preparation process is the same as Example 1, except that the calcination temperature in step (3) is changed to 1100°C.

[0103] The same method as in Example 1 was used to prepare the perovskite-type catalyst SrCoO 3-δ (1100℃)(0<δ≤0.5) in an environment with relative humidity RH=50% humidity and 500ppm ozone concentration for 3h to obtain the in-situ surface modified perovskite catalyst SrCoO 3-δ -O(1100℃)(0<δ≤0.5). The results show that the catalyst has the ability to efficiently decompose ozone at room temperature. The test results and the corresponding specific surface area are shown in Table 1 below.

[0104] Comparative Example 2

[0105] Chinese patent CN107376926A discloses a LaFeO3 perovskite-type ozone catalyst prepared by a citric acid sol-gel method. For better comparison, a reference catalyst was prepared according to the synthesis method disclosed in Chinese patent CN107376926A. The synthesis method of the reference catalyst is as follows:

[0106] (1) Lanthanum nitrate, ferric nitrate, and citric acid were dissolved in deionized water at a molar ratio of 1:1:2, and stirred to dissolve to obtain a mixed solution with a lanthanum nitrate concentration of 1 mol / L; ammonia water was slowly added dropwise to the mixed solution to adjust the pH value of the solution to 6.5, during which the solution gradually changed from reddish brown to a yellow-green sol; the sol was transferred to a 70°C oil bath and stirred for 4 hours to form a yellow-green gel;

[0107] (2) The gel obtained in step (1) is transferred to a porcelain boat and placed in a constant temperature drying oven at 130° C. for 12 h, and the yellow-green gel turns into a dark green xerogel; after the xerogel is formed, the material is ignited at its edge, and the material undergoes self-propagating combustion, during which the material gradually turns into yellow coral-like particles and releases a large amount of ammonia; after the combustion is completed, the sample generated by the self-propagating combustion is ground into powder;

[0108] (3) The powder obtained in step (2) is placed in a tube furnace, heated to 600° C. at a heating rate of 2° C. / min, and calcined for 2 h to obtain an active component with a structural formula of LaFeO 3 , which is in the form of a yellow powder.

[0109] Example 8: Application of in-situ surface-modified perovskite catalysts in ozone decomposition

[0110] The catalytic performance of an in-situ surface-modified perovskite catalyst was tested in a constant temperature and humidity environment. A constant temperature and humidity chamber, a gas distribution device, and an ozone generator were used to achieve intermittent temperature and humidity changes. The flow rate and concentration could also be adjusted, maintaining a constant level over a certain period of time. The ozone concentration was measured every 5 seconds using an ozone detector, and the ozone conversion rate was calculated. The in-situ modified perovskite catalysts prepared in Examples 1-7 and Comparative Example 1, as well as the reference catalysts prepared in Comparative Examples 1 and 2, were used to decompose ozone pollutants at room temperature. The specific reaction conditions were as follows:

[0111] First, the catalyst is granulated and particles with a particle size of 40-60 mesh are selected as ozone catalysts.

[0112] The catalyst was placed in a reaction tube with a specific amount of 100 mg of catalyst. A mixed gas containing 100 ppm of ozone was introduced into the reaction tube. In order to make the test gas flow smoother and reduce the diffusion pressure, the gas flow rate was 1 L / min. The reaction space velocity was 600,000 ml·g -1 ·h -1 The reaction temperature was 25°C (room temperature). An ozone detector was used to record the change in ozone concentration over time. The test duration was 4 hours, and ozone was defined as the average of the ozone concentration data collected during this period. The catalytic performance of each catalyst was tested at room temperature under humidity conditions of 20% and 90%.

[0113] Ozone conversion rate = (initial ozone concentration - residual ozone concentration) / initial ozone concentration, which is used to evaluate the utilization / treatment efficiency of various catalysts for the oxidant ozone.

[0114] Table 1 shows the specific surface area and ozone conversion efficiency of each catalyst group. Multiple tests demonstrated that the in-situ modified perovskite catalysts efficiently decompose ozone at room temperature under RH = 20% and RH = 90%. The final product of ozone conversion by the catalysts is oxygen, with no other byproduct gases produced.

[0115] Table 1 Ozone decomposition test results and corresponding specific surface areas of different catalysts at room temperature

[0116]

[0117] The test time of the in-situ modified perovskite catalyst in Example 1 was extended to 50 hours at room temperature and humidity RH = 20% to investigate the stability of the catalyst. Figure 7 As shown, the in situ surface modified perovskite catalyst SrCoO 3-δ (0<δ≤0.5) It still has efficient ozone removal ability after 50 hours and has excellent ozone decomposition catalytic stability.

[0118] From Table 1 and Figure 7 The results show that the prepared in situ surface modified perovskite catalyst SrCoO 3-δ (0<δ≤0.5) has excellent ozone catalytic degradation activity, and the effect remains at 100% in a 50-hour durability test at RH=20%. Furthermore, the effect still reaches above 80% in a 4-hour test at RH=90%.

[0119] The ozone degradation catalytic effect is also affected by a variety of factors such as the type, content, specific surface area, and degree of crystallinity of the active components. By changing the type and content of the active components (Examples 1-7), the ozone degradation effect of the catalyst can be adjusted. When transition metal elements are added to Mn / Fe, the catalyst specific surface area is increased, and the conversion rate under RH=90% is increased from 82.2% to 91.1%, 100% and 91.8 (Examples 2-4), proving that Mn / Fe can change the electronic structure around cobalt, affect the adsorption energy of ozone and intermediate oxygen species, and improve the adsorption energy of intermediate oxygen species to further enhance ozone degradation performance. When rare earth elements or alkaline earth metals are changed, Ce and Ba are appropriately added on the basis of Sr (Examples 5 and 6). The ozone conversion rate is not greatly improved, but it is still possible to achieve in-situ surface modification using ozone to enhance ozone catalytic degradation activity.

[0120] Although the in situ surface-modified perovskite catalyst prepared using ozone has excellent catalytic performance, the synthesis temperature will also affect the specific surface area and catalytic performance of the catalyst. When the synthesis temperature is increased to 1000°C (for example, 1100°C, Comparative Example 1), the specific surface area of ​​the catalyst is easily reduced, resulting in a decrease in effect; and the structural changes are not significant, so the performance improvement is not obvious (similar to Comparative Example 1).

[0121] Example 9: Application of in-situ surface-modified perovskite catalysts in ozone and VOC degradation

[0122] Benzene, propylene, methyl mercaptan and dichloromethane were used as typical VOC pollutants for testing and analysis.

[0123] The in-situ modified perovskite catalyst prepared in Example 1 was granulated, with a catalyst dosage of 200 mg and a particle size of 40-60 mesh. The granulated catalyst was placed in a reaction tube with an inner diameter of 4 mm, and an air flow containing a certain amount of ozone and VOC gas (150 ppm ozone gas, 10 ppm benzene gas) was introduced, with a carrier air flow rate of 100 mL / min and a reaction space velocity of 60,000 mL / (g·h). A constant temperature and humidity chamber, a gas distribution device, and an ozone generator were used to achieve intermittent temperature change, while the flow rate and concentration could be adjusted to maintain a constant value over a certain period of time. The CO2 concentration and organic matter concentration in the tail gas were detected by gas chromatograph (GC 9790Ⅱ, dual-channel FID detector, equipped with a methane reformer), and the VOC removal efficiency was calculated as follows:

[0124] VOC conversion rate = (initial VOC concentration - residual VOC concentration) / initial VOC concentration, which is used to evaluate the VOC treatment efficiency of various catalysts.

[0125] The test was carried out under the condition of room temperature and humidity RH = 20% according to the above method. The results are as follows Figure 9 As shown, the in situ surface modified perovskite catalyst SrCoO 3-δ (0<δ≤0.5) It has a highly efficient catalytic degradation capacity for VOC ozonation, maintaining a conversion rate of 75% after 10 hours of catalytic conversion. In addition, an ozone detector (3S-J5000, Tonglin Ozone) was used to monitor ozone concentration, confirming that no ozone leakage at the tail end would cause secondary pollution.

[0126] A control group 1 was set up. At 25°C, an empty reaction tube was tested for 4 hours with ozone plus VOC (150 ppm ozone gas, 10 ppm benzene gas). The average benzene concentration in the 4 hours was 7.48 ppm. Figure 8 shown.

[0127] Comparing the results of the control group and the experimental group, it is shown that under the condition of no catalyst, a certain proportion of ozone gas can oxidize a small amount of VOC gas because of its strong oxidizing property, but the efficiency is extremely low; however, the experimental group showed a higher VOC conversion rate, indicating that the in situ surface modified perovskite catalyst A x B y Co z O v -O plays a key role in catalytic ozone oxidation of VOC technology.

[0128] The control group 2 was set up to eliminate the influence of catalyst adsorption. 3-δ In the presence of -O, only 10ppm of benzene gas was introduced for testing. The benzene concentration remained at around 10ppm. Figure 8 As shown, the above results prove that the catalyst has no adsorption effect on benzene, which further proves the advanced nature of the catalyst-catalyzed ozone oxidation VOC technology.

[0129] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing an in-situ surface-modified perovskite catalyst, characterized in that: First, the general formula A is synthesized x B y Co z O v The perovskite material with the general formula A x B y Co z O v The perovskite material was placed in an ozone environment for in-situ surface modification to obtain A x B y Co z O v -O; A is one or more rare earth metal elements or alkaline earth metal elements, B is one or more first transition series metal elements excluding cobalt, 0<x≤10, 0≤y≤10, 0<z≤10, 0<v≤30.

2. The method for preparing an in-situ surface-modified perovskite catalyst according to claim 1, wherein: A is one or more of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Be, Mg, Ca, Sr, Ba and Ra; B is one or more of Ti, V, Cr, Mn, Fe, Ni, Cu and Zn.

3. The method for preparing an in-situ surface-modified perovskite catalyst according to claim 1, wherein: A includes Sr; B includes Mn.

4. The method for preparing the in-situ surface-modified perovskite catalyst according to any one of claims 1 to 3, characterized in that: Here are the steps: Step 1: adding one or more of the A-site metal salts, one or more of the B-site metal salts, and a cobalt salt into deionized water to dissolve into a metal salt solution; Step 2: dissolving an organic complexing agent in a metal salt solution, heating and stirring until the mixture becomes gel-like; the molar ratio of the organic complexing agent to the metal salt in the metal salt solution is 1:0.2-5; Step 3: Dry the gel and calcine it in an oxygen-containing environment at 400-1000°C for 1-24 hours to obtain the perovskite catalyst A without in-situ modification. x B y Co z O v ; Step 4: A x B y Co z O v Place in an environment with relative humidity RH=20-95% humidity and ozone concentration of 10-1000ppm for in-situ modification for 0.1-10h to obtain A x B y Co z O v -O.

5. The method for preparing an in-situ surface-modified perovskite-type catalyst according to claim 4, wherein: In step 1, the anion forms of the A-site metal salt, the B-site metal salt and the cobalt salt include NO 3- 、Cl - 、SO3 2- 、SO4 2- OH - 、SiO3 2- PO4 3- 、CH3COO - 、CO3 2- 、HCO3 - 、C2O4 2- One or more of.

6. The method for preparing an in-situ surface-modified perovskite-type catalyst according to claim 4, wherein: The organic complexing agent is one or more of ethylenediaminetetraacetic acid, ascorbic acid, citric acid, ketoxime, hydroxymethyl urea, dimethyl sulfoxide, diethyl dithiocarbamate, ethanedinitrile, ethylene glycol dimethyl phosphate, ethylene glycol diisopropyl phosphate, ethylene glycol diethyl phosphate, tri(methyl)phosphoric acid hydroxide, tri(isopropyl)phosphoric acid hydroxide and tri(ethyl)phosphoric acid hydroxide.

7. The method for preparing an in-situ surface-modified perovskite catalyst according to claim 4, wherein: In step 2, the mixture is stirred at a speed of 300 to 500 rpm and a temperature of 70 to 95° C. until the deionized water in the solution is evaporated to form a gel.

8. The in-situ surface-modified perovskite-type catalyst prepared by the method for preparing the in-situ surface-modified perovskite-type catalyst according to any one of claims 1 to 7.

9. The in-situ surface-modified perovskite catalyst according to claim 8, characterized in that: For SrCoO 3–δ -O, SrMn 0.4 Co 0.6 O 3–δ -O, SrMn 0.6 Co 0.4 O 3–δ -O, SrFe 0.2 Co 0.8 O 3–δ -O, Sr 0.9 Ce 0.1 CoO 3–δ -O, Sr 0.5 Ba 0.5 CoO 3–δ -O and Sr 0.9 Ce 0.1 Mn 0.5 Co 0.5 O 3–δ -O, one of them, 0 < δ ≤ 0.

5.

10. Use of the in-situ surface-modified perovskite catalyst according to claim 8 or 9 in room-temperature catalytic decomposition of ozone or room-temperature catalytic ozonation of VOCs.

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