Preparation method of low-temperature high-crystalline samarium calcium cobaltite perovskite type oxide and application thereof in catalytic oxidation of toluene

Abstract

The application belongs to the field of environmental catalysis technology, and relates to a preparation method of low-temperature high-crystalline samarium calcium cobaltite perovskite oxide and application of the low-temperature high-crystalline samarium calcium cobaltite perovskite oxide in catalytic oxidation of toluene. The preparation method comprises the following steps: step 1, dissolving samarium nitrate hexahydrate and cobalt acetate tetrahydrate in water to obtain a first solution, and dissolving citric acid monohydrate and urea in water to obtain a second solution; step 2, under the condition of stirring at room temperature, the second solution is added dropwise into the first solution to obtain a mixed metal salt solution; step 3, the mixed metal salt solution is heated to a preset temperature and stirred until a transparent wet gel is generated; step 4, the transparent wet gel is dried to obtain a foamed dry gel; and step 5, the foamed dry gel is ground into a powder, and the powder is calcined under an air atmosphere to obtain a powder solid phase. The low-temperature high-crystalline samarium calcium cobaltite perovskite oxide prepared by the application has the advantages of low energy consumption, low cost, large specific surface area, high crystallinity, high catalytic activity, good stability and strong water resistance.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis technology, and relates to a method for preparing samarium cobalt oxide perovskite type oxide at low temperature and its application in the catalytic oxidation of toluene. Background Technology

[0002] Volatile organic compounds (VOCs) refer to organic compounds with boiling points between 50°C and 260°C at atmospheric pressure, encompassing a variety of chemical substances including alkanes, alkenes, alkynes, and aromatic hydrocarbons. The main sources of VOCs include anthropogenic sources such as industrial emissions and fossil fuel combustion, as well as natural sources such as volcanic activity and forest fires. VOCs and NO... x Photochemical reactions can form secondary pollutants, leading to problems such as photochemical smog, the greenhouse effect, and ozone layer depletion, thus damaging the ecological environment. Furthermore, high concentrations of VOCs can disrupt the human nervous and respiratory systems, causing symptoms such as dizziness and nausea. In severe cases, they can affect genetic sequences, potentially causing cancer and birth defects.

[0003] Among numerous VOCs removal technologies, catalytic oxidation is considered one of the most promising due to its simple equipment and high purification efficiency. However, its development has been slow due to bottlenecks such as high reaction temperatures and poor long-term stability. In the catalytic oxidation of VOCs, surface defects (oxygen vacancies, cation defects) play a crucial role in gas adsorption and activation, and the content and regeneration of surface active oxygen species (adsorbed oxygen, lattice oxygen) are key factors affecting catalytic performance.

[0004] Cobalt-based perovskite oxides have attracted widespread attention due to their flexible composition, tunable electronic structure, stable physicochemical properties, and strong oxygen storage capacity. Their abundant lattice oxygen content provides theoretical support for the deep mineralization of VOCs. However, existing synthesis routes still face numerous technical challenges. High-temperature calcination in the preparation of cobalt-based perovskites results in stringent synthesis conditions, leading to significant energy consumption and problems such as small specific surface area, lack of surface defects, and insufficient activity of surface oxygen species. Lowering the calcination temperature inhibits crystal growth and crystallization, increasing disordered structures and severely affecting the thermal stability of the catalyst during high-temperature operation. These technical problems are key factors restricting the development of cobalt-based perovskite oxides as catalysts.

[0005] Therefore, in order to synthesize low-cost and high-performance samarium cobalt oxide perovskite and apply it to the field of efficient catalytic degradation of VOCs to ensure ecological environment safety and human health, there is an urgent need for a method for preparing samarium cobalt oxide with low temperature and high crystallinity. Summary of the Invention

[0006] In view of the above-mentioned technical problems, the present invention provides a method for preparing a low-temperature highly crystalline samarium cobalt oxide perovskite and its application in the catalytic oxidation of toluene. The present invention addresses two technical problems by considering the key factors restricting the development of cobalt-based perovskite oxide catalysts: (1) high calcination temperature causes particle sintering of the perovskite oxide, resulting in a small specific surface area and hindering the exposure of active sites; (2) low calcination temperature inhibits crystal growth and crystallization, leading to an increase in disordered structure and severely reducing the thermal stability of the catalyst during high-temperature operation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] The first aspect of this invention provides a method for preparing low-temperature, highly crystalline samarium cobalt oxide perovskite, the method comprising the following steps:

[0009] Step 1: Dissolve samarium nitrate hexahydrate and cobalt acetate tetrahydrate in water to obtain the first solution, and dissolve citric acid monohydrate and urea in water to obtain the second solution;

[0010] Step 2: Under stirring conditions at room temperature, add the second solution dropwise to the first solution to obtain a mixed metal salt solution;

[0011] Step 3: Heat the mixed metal salt solution to the preset temperature and stir until a transparent wet gel is formed;

[0012] Step 4: Dry the transparent wet gel to obtain a foamy dry gel;

[0013] Step 5: Grind the foamy dry gel into powder and calcine it in air atmosphere. The resulting powder solid phase is a low-temperature highly crystalline samarium cobalt perovskite oxide.

[0014] Furthermore, in step 1, the molar ratio of samarium nitrate hexahydrate to cobalt acetate tetrahydrate is 1:1.

[0015] Furthermore, in step 1, samarium nitrate hexahydrate and cobalt acetate tetrahydrate are the total metal salts, and the molar ratio of citric acid monohydrate to the total metal salts is 1:1.

[0016] Furthermore, in step 1, the molar ratio of urea to citric acid monohydrate is (1.5~1.75):1.

[0017] Furthermore, in step 3, the preset temperature is 80°C; in step 4, the drying temperature is 100°C and the drying time is 10 hours.

[0018] Furthermore, in step 5, the calcination temperature is 550°C and the calcination time is 2 hours.

[0019] The second aspect of this invention provides the application of a low-temperature, highly crystalline samarium cobalt oxide perovskite in the catalytic oxidation of toluene. This low-temperature, highly crystalline samarium cobalt oxide is prepared by any of the methods described in the first aspect, specifically, the low-temperature, highly crystalline samarium cobalt oxide is prepared at a toluene concentration of 1000 ppm and a mass hourly space velocity (WHSV) of 60000 mL·g. -1 ·h -1 It is applied under certain conditions.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) In the sol-gel process, the present invention introduces urea in situ, which has the following beneficial effects:

[0022] First, by adjusting the molar ratio of urea to citric acid monohydrate, the alkalinity in the solution system was directionally controlled, significantly improving the growth rate of samarium-cobalt crystals under low-temperature calcination conditions, and synthesizing low-temperature highly crystalline samarium cobalt perovskite oxide. Without affecting the sintering phenomenon, the introduction of urea significantly enhanced the crystallinity of the low-temperature calcined samarium cobalt perovskite oxide.

[0023] Second, during the stirring process at the preset temperature, the NH4 generated by the hydrolysis of urea in the sol-gel process... + NH4 occupies samarium sites in the perovskite lattice during the temperature-programmed heating stage. + Decomposition leads to the formation of samarium site defects. These defects optimize the electronic structure near cobalt sites on the perovskite, enhancing electron transfer and the ability to activate surface lattice oxygen. Furthermore, to maintain charge conservation in the catalyst system, samarium site defects also promote the formation of surface oxygen vacancies, enhancing the catalyst's adsorption and activation of gaseous oxygen.

[0024] The above two points demonstrate that the in-situ introduction of urea in this invention not only facilitates the synthesis of highly crystalline samarium cobalt perovskite oxides under low-temperature conditions, but also maintains and enhances the catalytic oxidation activity against VOCs.

[0025] (2) This invention defines samarium (Sm), a lanthanide metal among rare earth elements, as the A-site of ABO3-type perovskite oxides, with the following beneficial effects:

[0026] First, compared with existing technologies such as lanthanum cobalt perovskite, Sm 3+ The ionic radius (0.124 nm, coordination number 12) is slightly smaller than that of La. 3+ (0.136 nm, coordination number 12) is more conducive to the structural stability of perovskites, especially at high temperatures, it can reduce lattice mismatch and lattice distortion;

[0027] Second, Sm with a smaller ionic radius 3+It is compatible with the structure of cobalt-based perovskites, which significantly promotes the formation of oxygen vacancies and improves the catalytic performance of oxides;

[0028] Third, Sm 3+ It has a strong electron affinity, significantly affects the oxidation valence state of the active metal Co at the B site, regulates the electronic structure of cobalt-based perovskites, and makes them more electron-mobile, thereby enhancing their redox capabilities.

[0029] The above three points demonstrate that the samarium cobalt perovskite oxide of the present invention not only has stronger structural stability, but also maintains and enhances its catalytic oxidation ability for VOCs.

[0030] (3) The present invention limits the cobalt source to acetate, which has the following beneficial effects:

[0031] First, cobalt acetate has higher solubility, which ensures the uniformity of the precursor solution reaction process and helps to improve the disordered structure under low-temperature calcination conditions.

[0032] Second, the temperature at which cobalt acetate pyrolyzes to form cobalt oxide is lower, which helps to generate high-quality perovskite-type structures at lower temperatures.

[0033] Third, acetate is more environmentally friendly, mainly converting into CO2 and H2O, resulting in less secondary pollution and meeting the requirements of green chemistry.

[0034] The above three points demonstrate that the application of acetate as a cobalt source in this invention not only facilitates the synthesis of samarium cobalt perovskite oxides under low-temperature conditions, but also compensates for the environmental incompatibility of traditional processes.

[0035] (4) The beneficial effects of the samarium cobalt oxide perovskite synthesized in this invention are as follows:

[0036] First, under 80°C water bath stirring conditions, citric acid undergoes a polymerization reaction to form a high molecular polymer structure, which promotes the uniform distribution of samarium and cobalt in the structure (transparent wet gel).

[0037] Second, during the calcination process, non-metallic elements such as carbon and nitrogen are removed in gaseous form, while samarium, cobalt and oxygen undergo redox reactions and crystallize to form samarium cobalt perovskite oxide.

[0038] Third, during the calcination process, a large amount of gas is generated in the bulk phase, resulting in a rich mesoporous structure in the samarium cobalt perovskite oxide. By adjusting the temperature, the sintering phenomenon of the samarium cobalt perovskite oxide is significantly improved, the specific surface area is significantly increased, and more surface defects (oxygen vacancies and cation defects) are formed.

[0039] The above three points demonstrate that the samarium cobalt perovskite oxide of the present invention has a rich mesoporous structure, and temperature control effectively improves the sintering phenomenon, maintaining and enhancing the catalytic oxidation activity for VOCs.

[0040] (5) The application of the low-temperature, highly crystalline samarium cobalt oxide of the present invention as a catalyst for toluene degradation can efficiently catalyze the oxidation of toluene at higher toluene concentrations, higher mass hourly space velocities, and lower reaction temperatures, with the following beneficial effects:

[0041] First, excellent catalytic activity: at a toluene concentration of 1000 ppm and a mass hourly space velocity of 60000 mL·g -1 ·h -1 Under these conditions, the reaction temperature was gradually increased from room temperature to 280°C. The temperature at which the toluene conversion rate of the low-temperature highly crystalline samarium cobalt perovskite oxide reached 90% was 219°C, which was significantly lower than that of the samarium cobalt perovskite oxide before urea modification.

[0042] Second, good cyclic stability: at a toluene concentration of 1000 ppm and a mass hourly space velocity of 60000 mL·g -1 ·h -1 Under these conditions, after 5 cycles of testing, the temperature at which the toluene conversion of low-temperature, highly crystalline samarium cobalt oxide perovskite reached 90% only increased by 2.6°C.

[0043] Third, it exhibits excellent resistance to water poisoning: at a reaction temperature of 250°C, a toluene concentration of 1000 ppm, and a mass hourly space velocity of 60000 mL·g⁻¹. -1 ·h -1 Under the condition of a reaction system humidity of 3 vol.%, the toluene conversion rate of low-temperature highly crystalline samarium cobalt perovskite oxide remained above 92%; under the condition of a reaction system humidity of 5 vol.%, the toluene conversion rate remained above 88%.

[0044] Fourth, excellent long-term stability: at a reaction temperature of 250°C, a toluene concentration of 1000 ppm, and a mass hourly space velocity of 60000 mL·g. -1 ·h -1 Under these conditions, after 48 hours of continuous operation testing, the toluene conversion rate of low-temperature, highly crystalline samarium cobalt oxide perovskite-type oxide decreased by only 0.45%. Attached Figure Description

[0045] The present invention is described with reference to the following figures:

[0046] Figure 1 The catalytic activity spectra of the oxides prepared in Comparative Examples 1-3 for the oxidation of toluene are shown.

[0047] Figure 2The graphs show the catalytic oxidation activity of the oxides prepared in Examples 1-2 and Comparative Examples 4-7 for toluene oxidation.

[0048] Figure 3 The XRD patterns of the oxides prepared in Examples 1-2 and Comparative Examples 1-7 are shown.

[0049] Figure 4 Normalized peak intensities of oxide (121) crystal planes prepared for Examples 1-2, Comparative Example 1, and Comparative Examples 4-7;

[0050] Figure 5 FESEM images and particle size distribution diagrams of the oxides prepared in Example 1 are shown; wherein, Figure 5 a is a micron-level particle morphology feature diagram of the product; Figure 5 b is a surface morphology feature diagram of the product at the nanoscale; Figure 5 c represents the internal morphological features of the product at the nanoscale; Figure 5 d is Figure 5 Particle size distribution diagram of samarium cobaltate perovskite oxide in c;

[0051] Figure 6 FESEM images and particle size distribution of the oxide prepared for Comparative Example 1 are shown; among them, Figure 6 a is a micron-level particle morphology feature diagram of the product; Figure 6 b is a surface morphology feature diagram of the product at the nanoscale; Figure 6 c represents the internal morphological features of the product at the nanoscale; Figure 6 d is Figure 6 Particle size distribution diagram of samarium cobaltate perovskite oxide in c;

[0052] Figure 7 FESEM images and particle size distribution of the oxide prepared in Comparative Example 3 are shown; among them, Figure 7 a is a micron-level particle morphology feature diagram of the product; Figure 7 b is a surface morphology feature diagram of the product at the nanoscale; Figure 7 c represents the internal morphological features of the product at the nanoscale; Figure 7 d is Figure 7 Particle size distribution diagram of samarium cobaltate perovskite oxide in c;

[0053] Figure 8 EPR spectra of the oxides prepared in Example 1, Comparative Example 1, and Comparative Example 3;

[0054] Figure 9 H2-TPR spectra of the oxides prepared in Example 1, Comparative Example 1, and Comparative Example 3;

[0055] Figure 10O2-TPD-MS spectra of oxides prepared in Example 1, Comparative Example 1, and Comparative Example 3;

[0056] Figure 11 The toluene-TPD-MS (m / z=92) spectra of the oxides prepared in Example 1, Comparative Example 1, and Comparative Example 3 are shown; the inset shows the normalized area of ​​the toluene desorption peak on the three products near 75°C.

[0057] Figure 12 Toluene-TPD-MS (m / z=44) spectra of the oxides prepared in Example 1, Comparative Example 1, and Comparative Example 3;

[0058] Figure 13 The cyclic stability test spectrum of the oxide prepared in Example 1;

[0059] Figure 14 The water resistance test spectrum of the oxide prepared in Example 1;

[0060] Figure 15 The graphs show the long-term stability test results of the oxides prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0061] The technical solutions of this invention will now be clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0062] A method for preparing low-temperature, highly crystalline samarium cobalt oxide perovskite, comprising the following steps:

[0063] Step 1: Dissolve samarium nitrate hexahydrate and cobalt acetate tetrahydrate in water to obtain the first solution, and dissolve citric acid monohydrate and urea in water to obtain the second solution; the molar ratio of urea to citric acid monohydrate is (1.5~1.75):1; samarium nitrate hexahydrate and cobalt acetate tetrahydrate are total metal salts, and the molar ratio of citric acid monohydrate to total metal salts is 1:1;

[0064] Step 2: Under stirring conditions at room temperature, add the second solution dropwise to the first solution to obtain a mixed metal salt solution;

[0065] Step 3: Heat the mixed metal salt solution to 80°C and stir it in a water bath at this temperature until a transparent wet gel is formed;

[0066] Step 4: Dry the transparent wet gel at 100°C for 10 hours to obtain a foamy dry gel;

[0067] Step 5: Grind the foamy dry gel into powder and calcine it in air at a temperature of 550°C for 2 hours. The resulting powder solid phase is a low-temperature, highly crystalline samarium cobalt oxide perovskite.

[0068] In step 1, the molar ratio of samarium nitrate hexahydrate to cobalt acetate tetrahydrate is 1:1. Firstly, the chemical formula of samarium cobalt oxide perovskite is SmCoO3, where the theoretical stoichiometric ratio of the metal elements samarium (Sm) to cobalt (Co) is 1:1. Furthermore, the catalyst preparation process of this invention does not involve a washing step, thus eliminating the problem of metal element loss. Therefore, to obtain a high-purity SmCoO3 sample, the molar ratio of Sm to Co in the precursor should be 1:1, i.e., equal molar amounts of samarium nitrate hexahydrate (Sm(NO3)3·6H2O) and cobalt acetate tetrahydrate (Co(Ac)2·4H2O) should be weighed.

[0069] The above-mentioned low-temperature highly crystalline samarium cobalt oxide is used in the catalytic oxidation of toluene. This low-temperature highly crystalline samarium cobalt oxide is prepared by any one of the methods described in the first aspect. The low-temperature highly crystalline samarium cobalt oxide is used in a toluene concentration of 1000 ppm and a mass hourly space velocity (WHSV) of 60000 mL·g. -1 ·h -1 It is applied under certain conditions.

[0070] In the embodiments and accompanying drawings of the present invention:

[0071] SCO-U 1.75 -550 represents the oxide product prepared in Example 1;

[0072] SCO-U 1.5 -550 represents the oxide product prepared in Example 2;

[0073] SCO-550 represents the oxide product prepared in Comparative Example 1;

[0074] SCO-650 represents the oxide product prepared in Comparative Example 2;

[0075] SCO-750 represents the oxide product prepared in Comparative Example 3;

[0076] SCO-U1-550 represents the oxide product prepared in Comparative Example 4;

[0077] SCO-U2-550 represents the oxide product prepared in Comparative Example 5;

[0078] SCO-U 2.5 -550 represents the oxide product prepared in Comparative Example 6;

[0079] SCO-U3-550 represents the oxide product prepared in Comparative Example 7.

[0080] For ease of comparison, Comparative Examples 2 and 3 are based on Comparative Example 1 with a single factor substitution, replacing the calcination temperature in step 5; Comparative Examples 4 to 7 are based on Example 1 with a single factor substitution, replacing the amount of urea used in step 1.

[0081] Example 1

[0082] Step 1: Dissolve 2.2224g of samarium nitrate hexahydrate and 1.2454g of cobalt acetate tetrahydrate in 20mL of deionized water to obtain the first solution; dissolve 2.1014g of citric acid monohydrate and 1.0511g of urea in 10mL of deionized water to obtain the second solution;

[0083] Step 2: While stirring in a 25°C water bath, add the second solution dropwise to the first solution to obtain a mixed metal salt solution;

[0084] Step 3: Heat the water bath to 80°C and continuously stir the metal salt solution until a transparent wet gel is formed;

[0085] Step 4: Transfer the wet gel to a forced-air drying oven and dry at 100°C for 10 hours to obtain a dry gel;

[0086] Step 5: Grind the dry gel into powder and place it in a muffle furnace. Calcinate at 550°C for 2 hours in air atmosphere, with a heating rate of 2°C / min. -1 After the furnace temperature naturally cools to room temperature, the resulting samarium cobalt oxide perovskite is designated as SCO-U. 1.75 -550.

[0087] Example 2

[0088] The difference between Example 2 and Example 1 is that in step 1, 2.1014 g of citric acid monohydrate and 0.9009 g of urea were dissolved in 10 mL of deionized water to obtain a second solution; other conditions were the same as in Example 1, and the resulting samarium cobalt oxide perovskite was designated SCO-U. 1.5 -550.

[0089] Comparative Example 1

[0090] Comparative Example 1 provides a method for preparing samarium cobalt oxide perovskite, the specific steps of which include:

[0091] Step 1: Dissolve 2.2224g of samarium nitrate hexahydrate and 1.2454g of cobalt acetate tetrahydrate in 20mL of deionized water to obtain the first solution; dissolve 2.1014g of citric acid monohydrate in 10mL of deionized water to obtain the second solution;

[0092] Step 2: While stirring in a 25°C water bath, add the second solution dropwise to the first solution to obtain a mixed metal salt solution;

[0093] Step 3: Heat the water bath to 80°C and continuously stir the metal salt solution until a transparent wet gel is formed;

[0094] Step 4: Transfer the wet gel to a forced-air drying oven and dry at 100°C for 10 hours to obtain a foamy dry gel;

[0095] Step 5: Grind the dry gel into powder and place it in a muffle furnace. Calcinate at 550°C for 2 hours in air atmosphere, with a heating rate of 2°C / min. -1 After the furnace temperature naturally cools down to room temperature, the resulting samarium cobalt perovskite oxide is designated as SCO-550.

[0096] Comparative Example 2

[0097] The difference between Comparative Example 2 and Comparative Example 1 is that in step 5, the calcination temperature is changed to 650°C, while the other conditions are exactly the same as those in Comparative Example 1; and the resulting samarium cobalt perovskite oxide is denoted as SCO-650.

[0098] Comparative Example 3

[0099] The difference between Comparative Example 3 and Comparative Example 1 is that in step 5, the calcination temperature is changed to 750°C, while the other conditions are exactly the same as those in Comparative Example 1; and the resulting samarium cobalt perovskite oxide is denoted as SCO-750.

[0100] Comparative Example 4

[0101] The difference between Comparative Example 4 and Example 1 is that in step 1, 2.1014 g of citric acid monohydrate and 0.6006 g of urea were dissolved in 10 mL of deionized water to obtain a second solution; other conditions were the same as in Example 1, and the resulting samarium cobalt perovskite oxide was designated as SCO-U1-550.

[0102] Comparative Example 5

[0103] The difference between Comparative Example 5 and Example 1 is that in step 1, 2.1014 g of citric acid monohydrate and 1.2012 g of urea were dissolved in 10 mL of deionized water to obtain a second solution; other conditions were the same as in Example 1, and the resulting samarium cobalt perovskite oxide was designated as SCO-U2-550.

[0104] Comparative Example 6

[0105] The difference between Comparative Example 6 and Example 1 is that in step 1, 2.1014 g of citric acid monohydrate and 1.5015 g of urea were dissolved in 10 mL of deionized water to obtain a second solution; other conditions were the same as in Example 1, and the resulting samarium cobalt oxide perovskite was designated SCO-U. 2.5 -550.

[0106] Comparative Example 7

[0107] The difference between Comparative Example 7 and Example 1 is that in step 1, 2.1014 g of citric acid monohydrate and 1.8018 g of urea were dissolved in 10 mL of deionized water to obtain a second solution; other conditions were the same as in Example 1, and the resulting samarium cobalt perovskite oxide was designated as SCO-U3-550.

[0108] In Examples 1, 2, and Comparative Examples 1 to 7, the catalysts were tested for their catalytic oxidation performance of toluene. The test methods and conditions are as follows:

[0109] The specific conditions for the activity evaluation test are as follows: the product prepared in the examples or comparative examples is a catalyst, the mass of the catalyst is 100 mg (40-60 mesh), and the total flow rate is 100 mL·min. -1 (20% O2 / 80% N2), mass hourly space velocity (MHV) of 60,000 mL·g -1 ·h -1 The toluene concentration was 1000 ppm; the catalytic oxidation activities of toluene corresponding to the above examples and comparative examples are shown in Table 1.

[0110] Table 1. Comparison of catalytic oxidation activity of toluene in various examples and comparative examples.

[0111]

[0112] From Table 1, Figure 1 and Figure 2 It can be seen that the samarium cobalt oxide perovskite prepared in this invention has excellent catalytic oxidation activity for toluene, at a toluene concentration of 1000 ppm and a mass hourly space velocity of 60000 mL·g. -1 ·h -1 Under the specified conditions, the reaction temperature (T) at which the toluene conversion rate of Examples 1, 2, and Comparative Examples 1 to 7 reached 90% was determined. 90 All were below 250°C. Among them, Comparative Examples 1, 2, and 3, prepared by controlling the calcination temperature, had a T... 90 The calcination temperatures were 234°C, 237°C, and 247°C, respectively. It can be seen that the catalytic activity of Comparative Example 1, which was calcined at a temperature of 550°C, was significantly enhanced.

[0113] Furthermore, in Example 1, samarium cobalt oxide with low-temperature high crystallinity was prepared by in-situ introduction of urea at a toluene concentration of 1000 ppm and a mass hourly space velocity of 60000 mL·g. -1 ·h -1 Under certain conditions, it exhibits better catalytic oxidation activity of toluene, wherein the reaction temperature T 10 The temperature is 207°C, T 50 The temperature is 214°C, T 90 The temperature is 219°C.

[0114] like Figure 3 As shown in the XRD patterns of Examples 1, 2, and Comparative Examples 1 to 7, except for Comparative Example 4, the cobalt-based perovskite oxides prepared in this invention are all high-purity samarium cobalt oxide perovskite (XRD standard card PDF number for SmCoO3: 96-152-1745), with no obvious impurity phases. Comparing Comparative Examples 1, 2, and 3, Comparative Example 1 used a lower calcination temperature, resulting in a significant decrease in the intensity of the catalyst's diffraction peaks, indicating that it has the lowest crystallinity. Combined with the activity data in Table 1, the temperature specified in Comparative Example 1 is more conducive to improving the catalytic activity of samarium cobalt oxide perovskite for the oxidation of toluene.

[0115] Furthermore, comparing Examples 1, 2, and 4 to 7, it is evident that the introduction of urea resulted in significant differences in the diffraction peak intensities of samarium cobalt oxide perovskite. For example... Figure 4As shown, by quantitatively comparing the normalized diffraction peak intensity trends of the (121) crystal plane of Examples 1, 2, 4 to 7, it can be seen that Comparative Example 4 exhibits obvious samarium trioxide (Sm2O3 XRD standard card PDF number: 96-153-7837) and cobalt tetroxide (Co3O4 XRD standard card PDF number: 00-009-0418) impurities. This is attributed to the introduction of low-dose urea breaking the original complexation state between citric acid and metal ions, resulting in uneven distribution of metal ions in the polymer. In addition, compared with Comparative Example 1, the diffraction peak intensity of Comparative Example 4 is significantly reduced, indicating that a lower urea content inhibits the growth rate of perovskite crystals. With the increase of urea content, the diffraction peak intensity shows a volcano curve trend, with Example 1 having the highest peak intensity, which is 1.5 times that of Comparative Example 1. Obviously, an appropriate amount of urea is beneficial to the crystal growth of samarium cobalt oxide perovskite during low-temperature calcination. As shown in Comparative Examples 5 to 7, when the amount of urea exceeded 1.75 times that of citric acid monohydrate, the crystallinity showed a decreasing trend, and excessively high alkalinity significantly inhibited crystal growth. As shown in Table 1, the catalytic oxidation activity data for toluene showed that by utilizing urea to regulate the alkalinity of the system, crystal formation at low temperatures was accelerated. The favorable crystal structure promoted the formation and activation of surface lattice oxygen, thereby improving the catalytic activity. Example 1 exhibited the best catalytic performance compared to other examples and comparative examples. 10 T 50 and T 90 The temperatures at which catalytic activity is lowest are all observed.

[0116] The physical properties of the catalyst prepared in this invention were compared using field emission scanning electron microscopy and a specific surface area analyzer. A comparison of the FESEM images from Example 1, Comparative Example 1, and Comparative Example 3 shows that, as... Figure 5 a, Figure 6 a and Figure 7 As shown in a, the samarium cobalt oxide perovskite type oxides prepared by this invention are all irregular particles.

[0117] like Figure 5 b、 Figure 6 b and Figure 7 As shown in b, the surface morphology of the catalyst is... Figure 7 In Comparative Example 3 (b), obvious cracks appeared on the surface due to stress release, indicating that high-temperature calcination led to sintering. Figure 5 b and Figure 6 As shown in b, both Example 1 and Comparative Example 1 exhibit dense small particle accumulation and rich pore structure on their surfaces, showing no significant difference. This proves that the introduction of urea not only enhances the crystallinity of the crystals but also avoids the sintering of highly crystalline samples.

[0118] like Figure 5 c. Figure 6 c and Figure 7 Comparative analysis of the internal morphology shown in c reveals that the samarium cobaltate perovskite oxides prepared in this invention all exhibit a granular cluster structure. Furthermore, as shown in c... Figure 5 d、 Figure 6 d and Figure 7 As shown in Figure d, the average particle size distribution of Example 1 fluctuates around 47.8 nm, that of Comparative Example 1 fluctuates around 42.5 nm, while the particle size distribution of Example 3 fluctuates around 140.9 nm. It is evident that Examples 1 and Comparative Example 1 exhibit significantly smaller average particle sizes than Comparative Example 3. This indicates that Example 1 demonstrates a significant anti-sintering effect during the synthesis process, effectively suppressing the sintering phenomenon of samarium cobalt perovskite oxide, thereby significantly improving catalytic performance.

[0119] Table 2 Physical structural parameters of the catalysts in Example 1 and Comparative Examples 1 and 3

[0120]

[0121] As shown in Table 2, Example 1 and Comparative Example 1 have similar physical structural characteristics in terms of specific surface area, pore volume, and average pore size, and both are significantly higher than those of Comparative Example 3. This indicates that controlling the calcination temperature suppressed sintering, and the introduction of urea, while enhancing the crystallinity of low-temperature calcination, did not affect the physical properties. The optimized physical structural characteristics facilitate the formation of surface defects in samarium cobalt oxide perovskite oxides, the exposure of surface active sites, and the diffusion, adsorption, and activation of reactant gases, thereby improving the catalytic oxidation performance of toluene. Furthermore, compared to Comparative Example 1, while possessing the aforementioned excellent characteristics, the oxide product prepared in Example 1 further reduces the content of disordered structures, which helps to enhance the long-term stability of the catalyst under sustained high-temperature conditions.

[0122] Table 3. Atomic percentage of samarium in the whole sample and on the sample surface, and percentage of samarium defects on the surface in Examples 1, Comparative Examples 1 and 3.

[0123]

[0124] In Table 3 above:

[0125] a The ratio was obtained based on inductively coupled plasma optical emission spectroscopy (ICP-OES), and the ratio represents the atomic percentage of samarium in the overall sample.

[0126] b The ratio was obtained based on energy-dispersive X-ray spectroscopy (EDS), and the ratio represents the atomic percentage of samarium metal on the sample surface.

[0127] c: The difference between the theoretical atomic percentage (0.5) and the surface atomic percentage of metallic samarium.

[0128] The samarium content of the catalyst, both in its bulk and on its surface, was quantitatively analyzed using ICP-OES and EDS, respectively. As shown in Table 3, compared to Comparative Example 3 (where the atomic percentage of samarium remained largely unchanged) and Comparative Example 1 (where the change was minimal), the samarium content in Example 1 decreased from a bulk atomic percentage of 0.489 to a surface atomic percentage of 0.376. This significant reduction in surface samarium content indicates the formation of more A-site samarium defects on the SmCoO3 perovskite surface after calcination and urea modification. In particular, Example 1 exhibited the highest surface samarium defect percentage at 0.124, which facilitates the exposure of the active cobalt metal at the B-site, thereby improving catalytic activity. Furthermore, A-site samarium defects help regulate surface electronic properties, enhance electron migration, and promote the valence state cycling of cobalt ions during redox reactions. And the activation of the reactant gases, thereby enhancing the catalytic oxidation performance of toluene.

[0129] like Figure 8 As shown, the electron paramagnetic resonance spectra of Comparative Example 3, Comparative Example 1, and Example 1 exhibit a significant symmetrical signal (unpaired electrons located on surface oxygen vacancies) near g=2.003. It is evident that Example 1, with its greater number of surface oxygen vacancies, enhances the adsorption and activation of gaseous oxygen, converting it into surface-active oxygen species. This results in a significantly stronger signal in Example 1 compared to Comparative Example 1 and Comparative Example 3, thereby enhancing the catalytic oxidation activity of toluene.

[0130] also, Figure 9 and Figure 10 Hydrogen temperature-programmed reduction and oxygen temperature-programmed desorption experiments were presented for three different oxide catalysts. Example 1 showed lower Co content. 3+ The reduction temperature (339°C) and the surface lattice oxygen desorption temperature (418°C) indicate that redox reactions are more readily occurring on the surface of Example 1, and that surface lattice oxygen migrates more easily and undergoes oxidation with adsorbed toluene. The activity of the surface lattice oxygen was further verified by a toluene temperature-programmed desorption experiment. Figure 11 As shown, Example 1 exhibits a stronger toluene adsorption capacity, thereby improving the activation performance of toluene. Furthermore, the adsorbed toluene undergoes an oxidation reaction with surface-active lattice oxygen and is degraded into CO2 and H2O. Figure 12 As shown, the lower CO2 formation peak temperature (i.e., 261°C) in Example 1 demonstrates its stronger surface lattice oxygen activity.

[0131] In summary, the SCO-U prepared in Example 1 1.75-550 oxides possess a larger specific surface area and a higher content of surface defects, thereby promoting the adsorption and activation of reactant gases; superior low-temperature reducing properties and stronger surface lattice oxygen activity all contribute to the increased efficiency of deep mineralization of toluene on the catalyst surface. Therefore, the catalytic oxidation performance of toluene is significantly enhanced.

[0132] The stability of the oxide catalysts in Example 1 and Comparative Example 1 was also tested.

[0133] Specifically, Example 1 underwent cyclic stability and water resistance tests, while both Example 1 and Comparative Example 1 underwent long-term stability tests.

[0134] The cycle stability test was performed 5 times.

[0135] The water resistance test lasted for 18 hours, and the test was conducted alternately at 3 vol.% and 5 vol.% volume humidity.

[0136] The long-term stability test lasted for 48 hours.

[0137] The test temperature for water resistance and long-term stability was 250°C.

[0138] Other testing conditions are the same as those for the activity evaluation test.

[0139] The test results are shown in Table 4 below, and Figure 13 , Figure 14 and Figure 15 As shown.

[0140] Table 4. Stability of catalytic oxidation of toluene in Comparative Example 1 and Example 1

[0141]

[0142] From the above table 4 and Figure 13 As shown, the cyclic stability test results of the oxide catalyst indicate that after 5 cycles, the catalytic activity of the oxide prepared in Example 1 showed no significant change. 90 The temperature increased by only 2.6°C, which is Figure 13 The difference between 223.5°C and 220.9°C indicates that the oxide catalyst possesses excellent cycle stability.

[0143] From the above table 4 and Figure 14 As shown, under conditions of 3 vol.% or 5 vol.% volumetric humidity, the toluene conversion of the oxide catalyst prepared in Example 1 remained above 92% or 88%, and the toluene conversion could be rapidly restored to its initial state after the volumetric humidity was removed. These results indicate that the oxide product of Example 1 exhibits excellent water resistance.

[0144] From the above table 4 and Figure 15 As shown, the low-temperature highly crystalline samarium cobalt oxide prepared by low-temperature calcination and urea modification in Example 1 has excellent long-term stability, while the low-crystalline samarium cobalt oxide obtained by low-temperature calcination in Comparative Example 1 shows a significant deactivation trend during long-term high-temperature operation.

[0145] It can be seen that under high concentration toluene and high volumetric humidity conditions, the SCO-U prepared in Example 1... 1.75 -550 can achieve long-term, efficient, and stable catalytic oxidation of toluene, thus enabling its long-term application in the treatment of gas emissions containing high concentrations of toluene and high humidity. The above results demonstrate that this invention significantly improves the thermal stability of the oxide catalyst by introducing urea in step 1 (sol-gel process) to enhance the crystallinity of samarium cobalt oxide perovskite during low-temperature calcination.

[0146] In summary, the low-temperature, highly crystalline samarium cobalt oxide prepared by this invention not only has advantages such as low energy consumption, low cost, large specific surface area, high crystallinity, high catalytic activity, and strong water resistance, but also possesses excellent cycle stability and long-term stability, making it easy to apply in practice. It does not introduce secondary pollutants and has important practical value for the efficient catalytic purification of VOCs (such as toluene) in industrial waste gas.

Claims

1. A method for preparing a low-temperature, highly crystalline samarium cobalt oxide perovskite, characterized in that, The preparation method includes the following steps: Step 1: Dissolve samarium nitrate hexahydrate and cobalt acetate tetrahydrate in water to obtain the first solution, and dissolve citric acid monohydrate and urea in water to obtain the second solution; In step 1, samarium nitrate hexahydrate and cobalt acetate tetrahydrate are total metal salts, and the molar ratio of citric acid monohydrate to the total metal salts is 1:

1. In step 1, the molar ratio of urea to citric acid monohydrate is (1.5~1.75):1; Step 2: Under stirring conditions at room temperature, add the second solution dropwise to the first solution to obtain a mixed metal salt solution; Step 3: Heat the mixed metal salt solution to the preset temperature and stir until a transparent wet gel is formed; Step 4: Dry the transparent wet gel to obtain a foamy dry gel; Step 5: Grind the foamy dry gel into powder and calcine it in air atmosphere. The resulting powder solid phase is a low-temperature highly crystalline samarium cobalt perovskite oxide. In step 5, the calcination temperature is 550°C.

2. The preparation method according to claim 1, characterized in that, In step 1, the molar ratio of samarium nitrate hexahydrate to cobalt acetate tetrahydrate is 1:

1.

3. The preparation method according to claim 1, characterized in that: In step 3, the preset temperature is 80°C; In step 4, the drying temperature is 100°C and the drying time is 10 hours.

4. The preparation method according to claim 1, characterized in that: In step 5, the calcination time is 2 hours.

5. The application of a low-temperature highly crystalline samarium cobalt oxide perovskite in the catalytic oxidation of toluene, wherein the low-temperature highly crystalline samarium cobalt oxide is prepared by the preparation method according to any one of claims 1 to 4, characterized in that... The low-temperature, highly crystalline samarium cobalt oxide was prepared at a toluene concentration of 1000 ppm and a mass hourly space velocity (WHSV) of 60000 mL·g. -1 ·h -1 It is applied under certain conditions.

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