Modified perovskite catalyst for catalytic oxidation of toluene and preparation method and application thereof

Abstract

The application provides a preparation method of a modified catalyst for catalyzing combustion of toluene, and comprises the following steps: dissolving lanthanum nitrate, cobalt nitrate and glucose in water and stirring to dissolve, transferring to a rotary evaporator, evaporating to form a honey-like wet gel, and transferring to an oven for drying; sending the dry gel into a muffle furnace for calcination to obtain a sample LaCoO3; placing the obtained sample into an acetic acid solution for stirring for a certain time, centrifuging, washing and drying to obtain an acid-treated sample LaCoO3-A; mixing the obtained acid-treated sample with urea, grinding, and sending into a muffle furnace for calcination to obtain an acid-alkali co-treated sample LaCoO3-A-B. The catalyst is modified through acid-alkali co-treatment, the surface defect structure of the catalyst is optimized, the surface acid-alkali point position of the catalyst is adjusted, the interface oxidation-reduction cycle is accelerated, and the catalytic performance of the catalyst is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of toluene catalysis, and more particularly to a modified perovskite catalyst for the catalytic combustion of toluene and its preparation method. Background Technology

[0002] Against the backdrop of the coordinated advancement of air pollution control and the "dual carbon" goal, the efficient purification of volatile organic compounds (VOCs), as key precursors to ozone pollution and secondary organic aerosols (SOA), has become one of the core tasks for ecological and environmental improvement. Toluene, a typical industrial VOC, is widely derived from coatings, printing, petrochemicals, and other fields. It is highly volatile, highly toxic, and bioaccumulative, not only causing respiratory diseases and nervous system damage in humans but also exacerbating regional complex air pollution. Catalytic oxidation technology, capable of completely converting toluene into CO2 and H2O at relatively low temperatures without secondary pollution, is considered the most promising VOCs treatment technology. However, the development of high-performance catalysts is the core bottleneck for the industrial application of this technology. Perovskite catalysts (ABO3), with their unique crystal structure advantages, are significantly cheaper than noble metal catalysts (such as Pt and Pd), but still suffer from poor low-temperature activity and high difficulty in large-scale preparation.

[0003] CN109647720B discloses a method for preparing a calcium-doped lanthanum cobalt oxide perovskite catalyst, using lanthanum salt, cobalt salt, and calcium salt as raw materials, citric acid as a complexing agent, and an ethanol-water mixture as a solvent, to obtain a precursor via a sol-gel method, which is then crushed to obtain the perovskite catalyst.

[0004] CN109675576B discloses a method for preparing an acid-modified calcium-doped lanthanum cobalt oxide perovskite catalyst. Citric acid treatment is used to optimize the structure of the calcium-doped lanthanum cobalt oxide perovskite catalyst and improve its catalytic activity.

[0005] The catalysts described above have shown some effectiveness in the catalytic oxidation of toluene; however, the synthesis of these catalysts is time-consuming and energy-intensive. Summary of the Invention

[0006] In view of the relevant problems in the background art, the present invention provides a method for preparing and modifying perovskite catalysts and their applications.

[0007] According to a first aspect of the present invention, a method for preparing a perovskite-type catalyst is provided, comprising the following steps: Step S1: Dissolve lanthanum nitrate, cobalt nitrate, and glucose in water and stir until dissolved. Transfer the solution to a rotary evaporator and evaporate until a honey-like wet gel is formed. Transfer the solution to an oven and dry to obtain a dry gel. Step S2: Calcine the dried gel in a muffle furnace to obtain sample LaCoO3; The LaCoO3 sample was sequentially acid-treated and dried, then mixed with urea, ground, and calcined; the acid treatment refers to stirring with an aqueous acetic acid solution for a certain period of time.

[0008] In some implementations, the method specifically includes the following steps: Step S1: Dissolve lanthanum nitrate, cobalt nitrate, and glucose in water and stir until dissolved. Transfer the solution to a rotary evaporator and evaporate until a honey-like wet gel is formed. Transfer the solution to an oven and dry to obtain a dry gel. Step S2: The dry gel is fed into a muffle furnace for calcination to obtain the catalyst sample LaCoO3; Step S3: Place the obtained perovskite catalyst sample into an aqueous acetic acid solution and stir for a certain period of time. Then, centrifuge, wash, and dry to obtain the acid-treated sample LaCoO3-A. Step S4: Mix the obtained acid-treated sample with urea, grind it, and then calcine it in a muffle furnace to obtain the perovskite catalyst sample LaCoO3-AB.

[0009] In one implementation method, in step S1, the molar ratio of lanthanum ions, cobalt ions, and glucose is 1:1:2.

[0010] In one implementation method, in step S1, the time for stirring and dissolving the drug is 20 minutes.

[0011] In one implementation method, in step S1, the water bath temperature of the rotary evaporator is 60°C and the rotation speed is 60 rpm.

[0012] In one implementation method, in step S1, the oven is heated to 80°C and kept at that temperature for 12 hours.

[0013] In one implementation method, in step S2, the calcination temperature in the muffle furnace is 500-1000℃, for example 550℃, 650℃, 750℃, 850℃, or 950℃; preferably 650℃-850℃, and more preferably 650℃, with a calcination time of 5 hours.

[0014] In one implementation method, in step S3, the concentration of the acetic acid aqueous solution is 1 mol / L, and the stirring time is 1 hour.

[0015] In one implementation method, in step S3, the oven drying temperature is 80°C and the drying time is 12 hours.

[0016] In one implementation method, in step S4, the mass ratio of acid-treated sample to urea is 1:4.

[0017] In one implementation method, in step S4, the calcination temperature in the muffle furnace is 400°C and the calcination time is 3 hours.

[0018] According to a second aspect of the present invention, the present invention provides an application of the titanium dioxide-type catalyst described in the first aspect for the catalytic degradation of toluene.

[0019] In some embodiments of the present invention, the catalyst catalytically degrades toluene at 210°C with a removal efficiency of over 90%.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention reduces the time required for the solution to form a sol-gel by using a rotary evaporator to pre-prepare wet gel, thereby increasing the synthesis rate of the catalyst, improving the synthesis efficiency, and saving energy.

[0021] (2) In this invention, LaCoO3 is etched on the surface using acetic acid to expose the La at the A site. 3+ Partial dissolution forms defect structures, which helps to increase the specific surface area of ​​the catalyst, accelerate the interfacial redox cycle, and promote oxygen activation and toluene adsorption-activation.

[0022] (3) The present invention uses urea to treat LaCoO3 with alkali to further regulate the catalyst surface, enhance the low-temperature reduction ability, increase the oxygen vacancies on the catalyst surface, optimize the adsorption-activation-desorption path, and enhance the adsorption efficiency of the catalyst surface.

[0023] (4) Compared with the prior art CN109647720B, this application can not only eliminate the introduction of Ca element, but also the catalyst prepared can achieve a removal rate of more than 90% of toluene at low temperature (210℃).

[0024] (5) Compared with the prior art CN109675576B, this application also eliminates the Ca element, and surprisingly finds that the acid-base synergistic treatment method of this invention enables the prepared catalyst to achieve excellent toluene removal effect at low temperature; that is, the acid and base have a synergistic effect. Attached Figure Description

[0025] Figure 1 This is a comparison chart showing the toluene removal efficiency of samples from various embodiments and comparative examples in this invention; Figure 2 This is a graph showing the toluene removal efficiency of the sample obtained in Example 1 of this invention. Detailed Implementation

[0026] Toluene removal rate test method: The test was conducted using a PC-1000 VOC reaction and generation apparatus. 0.25 g of catalyst sample was placed in a quartz tube with an inner diameter of 6 mm. The initial toluene concentration was 1000 ppm, and the gas hourly space velocity (GHSV) was 24000 h⁻¹. -1The toluene concentration was monitored before and after the reaction using a gas chromatograph equipped with an FID detector.

[0027] To verify the optimal process of the technical solution in this application, the applicant previously optimized the key parameters of the calcination temperature in step S1 using single-factor variable optimization (other parameters are the same as in Example 1), and set up multiple sets of comparative experiments to determine the lowest temperature (T) at which the removal efficiency reached 90%. 90 Using the evaluation criteria, the optimal parameter range defined in this application was obtained.

[0028]

[0029] The results of the parameter comparison test above show that when the calcination temperature is 650℃, 750℃, and 850℃, the catalyst products exhibit similar and excellent performance. When the calcination temperature is set at 650℃, the comprehensive performance reaches the optimal level, and the energy expenditure and overall cost are the most reasonable.

[0030] Example 1

[0031] 6.49 g of lanthanum nitrate hydrate, 5.82 g of cobalt nitrate hexahydrate, and 7.21 g of anhydrous glucose were dissolved in 250 ml of deionized water at a molar ratio of 1:1:2. After stirring at room temperature for 20 min, the solution was transferred to a rotary evaporator and distilled at 60 °C and 60 r / min to form a honey-like wet gel. The gel was then transferred to a crucible and dried in an oven at 80 °C for 12 h to form a dry gel.

[0032] The obtained dry gel was ground into powder and then calcined in a muffle furnace at 650℃ for 5 hours to obtain sample LaCoO3. The obtained LaCoO3 was transferred to a beaker, and 100 ml of a 1 mol / L acetic acid aqueous solution was added. The mixture was magnetically stirred at room temperature for 1 hour, centrifuged and washed, and then placed in an oven at 80℃ for 12 hours to obtain sample LaCoO3-A. The obtained LaCoO3-A was transferred to a mortar, and a certain amount of urea crystals was added (sample to urea crystals mass ratio 1:4). After grinding until completely homogeneous, the mixture was transferred to a crucible and calcined in a muffle furnace at 400℃ for 3 hours to finally obtain sample LaCoO3-AB.

[0033] Comparative Example 1

[0034] 6.49 g of lanthanum nitrate hydrate, 5.82 g of cobalt nitrate hexahydrate, and 7.21 g of anhydrous glucose were dissolved in 250 ml of deionized water at a molar ratio of 1:1:2. After stirring at room temperature for 20 min, the solution was transferred to a rotary evaporator and distilled at 60 °C and 60 r / min to form a honey-like wet gel. This gel was then transferred to a crucible and dried at 80 °C for 12 h to form a dry gel. The resulting dry gel was ground into powder and then calcined in a muffle furnace at 650 °C for 5 h to obtain the sample LaCoO3.

[0035] Comparative Example 2

[0036] 6.49 g of lanthanum nitrate hydrate, 5.82 g of cobalt nitrate hexahydrate, and 7.21 g of anhydrous glucose were dissolved in 250 ml of deionized water at a molar ratio of 1:1:2. After stirring at room temperature for 20 min, the solution was transferred to a rotary evaporator and distilled at 60 °C and 60 r / min to form a honey-like wet gel. This gel was then transferred to a crucible and dried at 80 °C for 12 h to form a dry gel. The resulting dry gel was ground into powder and calcined in a muffle furnace at 650 °C for 5 h to obtain sample LaCoO3. The LaCoO3 was then transferred to a beaker, and 100 ml of 1 mol / L acetic acid solution was added. After magnetic stirring at room temperature for 1 h, the mixture was centrifuged, washed, and then dried at 80 °C for 12 h to obtain sample LaCoO3-A.

[0037] Comparative Example 3

[0038] 6.49 g of lanthanum nitrate hydrate, 5.82 g of cobalt nitrate hexahydrate, and 7.21 g of anhydrous glucose were dissolved in 250 ml of deionized water at a molar ratio of 1:1:2. After stirring at room temperature for 20 min, the solution was transferred to a rotary evaporator and distilled at 60 °C and 60 r / min to form a honey-like wet gel. This gel was then transferred to a crucible and dried at 80 °C for 12 h to form a dry gel. The resulting dry gel was ground into powder and calcined in a muffle furnace at 650 °C for 5 h to obtain sample LaCoO3. A certain amount of urea crystals was added to the LaCoO3 in a mortar (sample to urea crystal mass ratio of 1:4). After grinding until completely homogeneous, the mixture was transferred to a crucible and calcined in a muffle furnace at 400 °C for 3 h to finally obtain sample LaCoO3-B.

[0039] like Figure 1 The figure shows the results of toluene removal efficiency for each sample at different temperatures: The results show that acid treatment, alkali treatment, and co-acid-alkali treatment all enhance catalyst performance. Among them, the co-acid-alkali treated sample LaCoO3-AB exhibits the best performance, with the lowest temperature (T90) at which the toluene removal efficiency reaches 90% being around 210℃. The perovskite catalyst after acid-alkali co-treatment demonstrates better performance. Reversing the order of acid and alkali treatments resulted in samples with essentially the same performance.

[0040] At a low temperature of 200℃, the removal efficiency of unmodified LaCoO3 for toluene was less than 20%, and the toluene conversion rates of acid-treated LaCoO3-A and alkali-treated LaCoO3-B samples were both less than 40%, while the toluene removal rate of the LaCoO3-AB sample treated with both acid and alkali reached over 50%. At 205℃, the removal efficiency of toluene by single modified and original catalysts was less than 50%, while the removal efficiency of LaCoO3-AB increased to over 75%.

[0041] It is evident that in the low-temperature range of 200℃ and 205℃, the acid-base co-modification strategy can significantly improve the low-temperature activity of perovskite catalysts and effectively reduce the temperature required for complete degradation of toluene. Compared with single acid-base modified and unmodified samples, it has low-temperature catalytic advantages.

[0042] The results of the toluene removal efficiency of the sample LaCoO3-AB prepared in Example 1 are as follows: Figure 2 As shown, the reaction temperature was 210℃, and the other test conditions were the same as above.

[0043] Depend on Figure 2 It can be seen that during the 24 hours of testing, the conversion rate of the catalyst sample to toluene remained above 90%, and there was no significant decrease in catalytic activity.

[0044] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a perovskite-type catalyst, comprising the following steps: Step S1: Dissolve lanthanum nitrate, cobalt nitrate, and glucose in water and stir until dissolved. Transfer the solution to a rotary evaporator and evaporate until a honey-like wet gel is formed. Transfer the solution to an oven and dry to obtain a dry gel. Step S2: Calcine the dried gel in a muffle furnace to obtain sample LaCoO3; The LaCoO3 sample was sequentially acid-treated and dried, then mixed with urea, ground, and calcined; the acid treatment refers to stirring with an aqueous acetic acid solution for a certain period of time.

2. The method according to claim 1, specifically includes the following steps: Step S1: Dissolve lanthanum nitrate, cobalt nitrate, and glucose in water and stir until dissolved. Transfer the solution to a rotary evaporator and evaporate until a honey-like wet gel is formed. Transfer the solution to an oven and dry to obtain a dry gel. Step S2: Calcine the dried gel in a muffle furnace to obtain sample LaCoO3; Step S3: Place the obtained perovskite catalyst sample into an aqueous acetic acid solution and stir for a certain period of time. Then, centrifuge, wash, and dry to obtain the acid-treated sample LaCoO3-A. Step S4: Mix the obtained acid-treated sample with urea, grind it, and then calcine it in a muffle furnace to obtain the perovskite catalyst sample LaCoO3-AB.

3. According to the method of claim 2, in step S2, the calcination temperature in the muffle furnace is 650℃-850℃.

4. According to the method of claim 2, in step S2, the calcination temperature in the muffle furnace is 650°C.

5. According to the method of claim 2, in step S1, the molar ratio of lanthanum ions, cobalt ions and glucose is 1:1:2; And / or, in step S1, the time for stirring and dissolving the drug is 20 minutes; And / or, in step S1, the water bath temperature of the rotary evaporator is 60°C and the rotation speed is 60 rpm; And / or, in step S1, the oven is heated to 80°C for 12 hours.

6. According to the method of claim 2, in step S3, the concentration of the acetic acid aqueous solution is 1 mol / L, and the stirring time is 1 hour; And / or, in step S3, the oven drying temperature is 80°C and the drying time is 12 hours.

7. According to the method of claim 2, in step S4, the mass ratio of the acid-treated sample to urea is 1:4; And / or, in step S4, the muffle furnace calcination temperature is 400℃ and the calcination time is 3 hours.

8. Use of a perovskite catalyst prepared by the method of claim 1 for the catalytic degradation of toluene.

9. According to claim 8, the catalyst catalyzes the degradation of toluene at 210°C with a removal efficiency of over 90%.

10. A method for preparing a perovskite-type catalyst for the catalytic degradation of toluene. Step S1: Dissolve lanthanum nitrate, cobalt nitrate, and glucose in water and stir until dissolved. Transfer the solution to a rotary evaporator and evaporate until a honey-like wet gel is formed. Transfer the solution to an oven and dry to obtain a dry gel. Step S2: The dry gel is placed in a muffle furnace and calcined at 650°C to obtain sample LaCoO3; Step S3: Place the obtained perovskite catalyst sample into an aqueous acetic acid solution and stir for a certain period of time. Then, centrifuge, wash, and dry to obtain the acid-treated sample LaCoO3-A. Step S4: Mix the obtained acid-treated sample with urea, grind it, and then calcine it in a muffle furnace to obtain the perovskite catalyst sample LaCoO3-AB.

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