Perovskite catalyst and method for producing the same
By introducing alkali metal complexing agents into the synthesis of perovskite catalysts, the conversion of NO into adsorbed NO2 is regulated, solving the problem of carbon soot oxidation at low temperatures and providing a low-cost, high-efficiency catalyst solution.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TIANJIN UNIV
- Filing Date
- 2024-04-28
- Publication Date
- 2026-06-23
AI Technical Summary
Existing catalysts are difficult to effectively oxidize carbon soot in diesel engine exhaust at low temperatures, and precious metal catalysts are expensive and have poor thermal stability. There is a lack of low-cost and efficient non-precious metal catalysts.
Alkali metals were introduced into the perovskite catalyst synthesis process using chelating agents. By controlling the type and content of the chelating agents, adsorbed NO2 was formed to promote carbon soot oxidation, thus preparing a perovskite catalyst with good redox ability and thermal stability.
It achieves efficient oxidation of carbon soot at low temperatures. The catalyst has excellent water and sulfur resistance and cycle stability. It is low in cost, simple to operate, and its catalytic activity even exceeds that of precious metals.
Smart Images
Figure CN118179478B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalysts, specifically relating to a perovskite catalyst and its preparation method. Background Technology
[0002] Carbon particulates are formed by the incomplete combustion of diesel fuel under high temperature and low oxygen conditions, and are a major cause of smog, the greenhouse effect, and ecological degradation. Therefore, reducing soot emissions is urgently needed. Diesel particulate filters (DPFs) are the most effective technology for capturing carbon particulates, but timely regeneration is essential to prevent carbon deposits from accumulating in the DPF orifices, leading to increased exhaust back pressure and affecting the normal operation of diesel engines. While carbon particulates can be removed through combustion under external heat above 600°C, to remove them at lower exhaust temperatures (150-400°C), a catalyst needs to be coated on the DPF surface to reduce the activation energy required for the carbon oxidation reaction.
[0003] Noble metal catalysts have been widely developed due to their excellent redox capabilities, but their high cost and poor thermal stability limit their practical applications. Therefore, designing efficient non-noble metal catalysts to accelerate carbon soot oxidation is a challenge. To date, various catalysts have been designed as low-cost alternatives, such as metal oxides, peroxides, spinels, and mullite. Among them, perovskites have emerged as the most promising candidate catalysts due to their good redox capabilities and thermal stability.
[0004] Alkali metals or alkaline earth elements are commonly used to enhance the catalytic activity of perovskite catalysts for soot oxidation. The use of alkaline earth metals to modify catalysts primarily improves their redox properties. Several papers have reported that alkali metals, due to their high fluidity, can enhance the contact between the catalyst and soot, thereby improving the catalyst's catalytic performance. Typically, alkali metals are introduced into the structure as dopants during synthesis or loaded onto the surface of the perovskite catalyst after synthesis; however, there are no reports of alkali metals being introduced into perovskite catalysts as complexing agents during synthesis. Furthermore, some researchers have investigated the effects of alkali metals as modifiers on the strength of nitrogen oxide adsorption and the conversion of nitrogen oxides to nitrogen dioxide. In addition, the influence of the presence of different nitrate intermediates on the catalytic activity of soot oxidation has not been adequately discussed in previous studies, and there is no conclusive evidence that any intermediate has a stronger ability to oxidize soot.
[0005] Currently, no method has been reported for introducing alkali metals using complexing agents during the synthesis of perovskite catalysts. For example, US20070105715A1 discloses a method for preparing a catalyst for a diesel particulate filter (DPF) suitable for capturing particulate matter (PM) in diesel engine exhaust. This novel catalyst uses a perovskite-type composite oxide as the active component and can promote the oxidation of particulate matter (PM) in diesel engine exhaust. It exhibits adsorption characteristics for nitrogen oxides (NO) in the temperature range of 200 to 450 degrees Celsius. Furthermore, this catalyst can promote the combustion of particulate matter at lower temperatures without the use of precious metals, helping to reduce the harmful effects of diesel engine emissions.
[0006] CN101683616 A discloses a novel method for preparing a catalyst for purifying diesel engine exhaust soot, employing rare earth metals, transition metals, and alkali metals as the active components of the catalyst. This catalyst possesses a macroporous structure and forms perovskite-type, perovskite-like, or spinel-type composite metal oxides. The active surface area of the catalyst is effectively utilized, reducing the combustion temperature of soot particles and thus improving the purification effect.
[0007] Although the catalysts mentioned above can all catalyze the oxidation of carbon soot particles, developing a low-cost catalyst that also possesses good catalytic activity and thermal stability remains a significant challenge. Summary of the Invention
[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a perovskite catalyst and its preparation method.
[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0010] A method for preparing a perovskite catalyst includes the following steps:
[0011] (1) Add metal ions to the deionized aqueous solution of the chelating agent; the metal ions are a mixture of lanthanum metal ions and transition metal ions; then add citric acid and stir until a clear solution is obtained.
[0012] (2) Gradually add ammonia solution to the mixture prepared in step (1) to adjust the pH value;
[0013] (3) After evaporating the water from the mixture obtained in step (2), the mixture is calcined at high temperature to obtain the perovskite catalyst.
[0014] The molar ratio of citric acid to metal ions is x, where 1 ≤ x ≤ 1.2;
[0015] The transition metal salt is one of cobalt nitrate hexahydrate, aluminum nitrate nonahydrate, manganese nitrate hexahydrate, and copper nitrate trihydrate.
[0016] The chelating agent is at least one of ethylenediaminetetraacetic acid (EDTA), disodium EDTA, or dipotassium EDTA; preferably disodium EDTA.
[0017] The molar ratio of the chelating agent to the metal ion is y, where 0 ≤ y ≤ 0.5; preferably, the molar ratio of the chelating agent to the metal ion is 1:10.
[0018] The molar ratio of the metal ions to the transition metal ions is 1:1.
[0019] In step (2), the pH value is 6.5-7.5.
[0020] In step (3), the conditions for high-temperature calcination are: calcination at 300-400℃ for 1-2 hours and calcination at 600-800℃ for 5-6 hours; preferably: calcination at 350℃ for 1-2 hours and calcination at 700℃ for 5-6 hours.
[0021] The present invention also includes a perovskite catalyst obtained by the preparation method described above.
[0022] Compared with the prior art, the beneficial effects of the present invention are:
[0023] This invention provides a catalyst capable of oxidizing soot in diesel engine exhaust gas at relatively low temperatures within the exhaust gas temperature range. It primarily achieves efficient soot oxidation by controlling the type and content of the complexing agent to convert NO into adsorbed NO2. X With the assistance of [the catalyst], the oxidation of adsorbed NO2 soot formed on the catalyst surface is promoted. The catalyst prepared by the method of this invention exhibits even stronger activity in oxidizing soot than that of precious metals. Moreover, this catalyst possesses excellent water and sulfur resistance as well as cycle stability, indicating that it can operate stably under complex conditions. Furthermore, the synthesis method is easy to operate and simple, possessing great potential for practical application.
[0024] This invention enables accelerated catalytic combustion of soot at low temperatures, maintaining essentially unchanged activity even under complex conditions involving both water vapor and sulfur dioxide. The method is simple to operate, does not use precious metals, and has a very low catalyst production cost. Adding a complexing agent containing alkali metals affects the lattice oxygen mobility of the lanthanum-based perovskite catalyst, as well as the types and conversion processes of intermediate nitrogen oxides adsorbed on the catalyst surface. This catalyst first effectively converts NO into monodentate nitrite, and then further into adsorbed NO2, thus oxidizing soot more efficiently. This simple method of adding a complexing agent containing alkali metals regulates the catalyst's redox capacity and the amount of NO adsorbed on the surface. x type. Attached Figure Description
[0025] Figure 1 The LaCoO3 catalyst synthesized with different complexing agents prepared in this invention is used in NO X Assisted carbon dioxide smoke spectrum;
[0026] Figure 2 The LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention are used in NO X Assisted carbon dioxide smoke spectrum;
[0027] Figure 3 These are carbon fumes oxidized by LaCoO3 catalysts synthesized with different complexing agents prepared in this invention under different gas conditions.
[0028] Figure 4 This is the carbon soot emission spectrum of the LaCoO3 perovskite catalyst prepared in this invention without the use of EDTA-2Na after 5 cycles of testing.
[0029] Figure 5 The NO-TPD spectra of LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention under NO atmosphere;
[0030] Figure 6 yes Figure 6 The NO-TPO spectra of LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention under NO and O2 atmospheres;
[0031] Figure 7 These are the in-situ DRIFT spectra of the LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention under NO and O2 atmospheres. Detailed Implementation
[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.
[0033] Example 1
[0034] A method for preparing a perovskite catalyst with low-temperature oxidation advantages specifically includes the following steps:
[0035] (1) Dissolve the chelating agent ethylenediaminetetraacetic acid (EDTA) in ammonia water (add a small amount of ammonia water to promote dissolution), then pour it into 150mL of deionized water, and continue stirring after it is completely dissolved.
[0036] (2) During continuous stirring, a mixture of lanthanum nitrate hexahydrate and cobalt nitrate hexahydrate in a molar ratio of 1:1 is added to the mixture prepared in step (1). Stirring continues until the mixture is completely dissolved. Finally, citric acid is added and stirred until a clear solution is obtained. The molar ratio of EDTA to metal ions is 1:10. The molar ratio of citric acid to metal ions is 1:1.
[0037] (3) During the continuous stirring process, gradually add ammonia solution to the mixture prepared in step (2) to adjust the pH value of the mixture to 7.5, and the solution can be obtained.
[0038] (4) Place the solution obtained in step (3) in a rotary evaporator and evaporate it at 65°C until all the water is evaporated. The resulting substance is in a dry state.
[0039] (5) The substance obtained in step (4) is placed in a muffle furnace for high-temperature calcination. The catalyst A for catalytic oxidation of diesel vehicle exhaust carbon soot is obtained by calcining at 350°C for 1 hour and 700°C for 5 hours under air conditions.
[0040] Example 2
[0041] A method for preparing a perovskite catalyst with low-temperature oxidation advantages is the same as that in Example 1, except that in step (1), dipotassium ethylenediaminetetraacetate (EDTA-2K) is dissolved in 150 mL of deionized water; in step (2), the molar ratio of EDTA-2K to metal ions is 1:10; and the subsequent steps are the same as in Example 1, so that catalyst B for catalytic oxidation of diesel vehicle exhaust carbon soot can be obtained.
[0042] Example 3
[0043] A method for preparing and applying a perovskite catalyst with low-temperature oxidation advantages is described. The basic steps are the same as in Example 1, except that in step (1), disodium ethylenediaminetetraacetate (EDTA-2Na) is dissolved in 150 mL of deionized water; in step (2), the molar ratio of EDTA-2Na to metal ions is 1:10; and the subsequent steps are the same as in Example 1, thus obtaining catalyst C for catalytic oxidation of diesel vehicle exhaust carbon soot.
[0044] Example 4
[0045] A method for preparing and applying a perovskite catalyst with low-temperature oxidation advantages is described. The basic steps are the same as in Example 1, except that in step (1), disodium ethylenediaminetetraacetate (EDTA-2Na) is dissolved in 150 mL of deionized water; in step (2), the molar ratio of EDTA-2Na to metal ions is 1:5; and the subsequent steps are as in Example 1, thus obtaining catalyst D for catalytic oxidation of diesel vehicle exhaust carbon soot.
[0046] Example 5
[0047] A method for preparing and applying a perovskite catalyst with low-temperature oxidation advantages is described. The basic steps are the same as in Example 1, except that in step (1), disodium ethylenediaminetetraacetate (EDTA-2Na) is dissolved in 150 mL of deionized water; in step (2), the molar ratio of EDTA-2Na to metal ions is 1:15; and the subsequent steps are the same as in Example 1, thereby obtaining catalyst E for catalytic oxidation of diesel vehicle exhaust carbon soot.
[0048] Comparative Example
[0049] The synthesis and application of a lanthanum cobalt perovskite catalyst without alkali metals and EDTA are based on the same steps as in Example 1, except that no chelating agent is added in step (1). The subsequent steps are as in Example 1, and the catalyst E for catalytic oxidation of diesel vehicle exhaust carbon soot can be obtained.
[0050] The catalysts prepared in Examples 1-5 were subjected to fixed-bed reaction with the following parameters: catalyst dosage: 0.1 g, soot: 0.01 g, silica: 0.03 g, catalyst particle size: 40-60 mesh, flue gas concentration: NO: 2000 ppm, O2 concentration: 10 vol l.%, N2: balance, total gas flow rate: 50 mL min⁻¹, and reaction temperature: 100-600 °C.
[0051] Figure 1 The LaCoO3 catalyst synthesized using different complexing agents prepared in this invention is used in NO X The carbon soot oxidation spectrum under the assistance of EDTA-2Na showed that when EDTA-2Na was used as a complexing agent in the synthesis of perovskite catalyst, the catalyst exhibited a significant advantage in carbon soot oxidation, that is, the presence of EDTA-2Na is beneficial to the improvement of catalyst activity.
[0052] Figure 2 The LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention are used in NO X Carbon soot spectroscopy was performed with the aid of EDTA-2Na; the results showed that with the increase of EDTA-2Na content, the combustion T of carbon soot decreased. 50The activity first decreased and then increased. When the molar ratio of EDTA-2Na to metal ions was 0.1, the catalyst showed an advantage in oxidizing carbon soot. This also indicates that the addition of EDTA-2Na has both positive and negative effects on the catalyst activity. Only an appropriate amount of EDTA-2Na can effectively promote the oxidation of carbon soot.
[0053] Figure 3 These are the carbon dioxide emission spectra of LaCoO3 catalysts synthesized with different complexing agents prepared in this invention under different gas conditions; the results show that when only 100 ppm SO2 is introduced into the gas, Example 1 ( Figure 3 Example a) and Example 2 ( Figure 3 T in b) 50 The temperatures were increased by 70 and 77°C respectively, in Example 3 ( Figure 3 T in c) 50 The reaction remained essentially unchanged. This indicates that Example 3 has strong sulfur resistance, and the catalyst activity was not significantly affected. When both water vapor and sulfur dioxide were introduced into the reaction gas, the catalytic activity of Examples 1 and 2 was still suppressed, but the catalytic performance of Example 3 was improved. 50 The temperature was lowered to 254°C, indicating that Example 3 has strong water and sulfur resistance and can be used under complex gas conditions.
[0054] Figure 4 This is the carbon soot oxidation spectrum of the LaCoO3 perovskite catalyst prepared by this invention without the use of EDTA-2Na (Figure a, comparative example) and Example 3 (Figure b) after 5 cycles of testing; the results show that after five cycles of testing, T 90 The temperature increased by 64°C, indicating that the catalyst's stability is relatively weak. The catalyst in Example 3, however, showed a temperature increase of 64°C. 90 The temperature only increased by 38°C, indicating that the addition of EDTA-2Na can improve the stability of the catalyst;
[0055] Figure 5 The images show the NO-TPD spectra of LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention under NO and NO2 atmospheres. With increasing EDTA-2Na content, the desorption capacity of the catalyst for NO also increases significantly. This is because the introduction of the alkali metal Na greatly improves the NO desorption capacity of the LaCoO3 catalyst. X The adsorption of NO by the catalyst surface, particularly the alkaline sites, is beneficial for the adsorption of the acidic gas NO. Furthermore, it was observed that the peak temperature of NO desorption in Example 4 was higher than that in Example 3. This indicates that a higher content of EDTA-2Na is beneficial for improving the NO adsorption strength.
[0056] Figure 6The images show the NO-TPO spectra of LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention under NO and NO2 atmospheres; in the comparative example and Example 3, the NO concentration first decreases and then increases. This phenomenon indicates that NO is initially adsorbed on the catalyst and then slowly reaches the NO adsorption-desorption equilibrium. When the NO concentration begins to increase, the temperature in Example 3 is higher than that in the comparative example, indicating that EDTA-2Na promotes the adsorption of NO on the catalyst, thereby allowing more NO to be adsorbed on the LaCoO3 surface. However, a different situation was observed in Example 4, where NO... X There was no significant increase. This may be because the excess EDTA-2Na enhanced the catalyst's adsorption capacity for nitrogen oxides, and the adsorption of NO in Example 4 did not reach saturation throughout the NO-TPO process.
[0057] Figure 7 This is an in-situ DRIFT spectrum of the LaCoO3 catalysts synthesized with different EDTA-2Na contents prepared in this invention under NO and O2 atmospheres. Figure a represents the comparative example, b represents Example 3, and c represents Example 4. The results show that the intermediate products formed after NO adsorption on the surface in the comparative example are nitro chemicals, which convert to gaseous NO2 with increasing temperature. The intermediates formed on the surface in Example 3 are monodentate nitrites, which convert to adsorbed NO2 with increasing temperature. However, the conversion of monodentate nitrites to gaseous NO2 adsorption in Example 4 is inhibited. The results indicate that adsorbed NO2 is a stronger NO auxiliary agent for carbon soot oxidation. X The species EDTA-2Na modifies the effect of catalysts on NO in the presence of oxygen. X The adsorption behavior affects the activity of the catalyst in oxidizing carbon soot.
[0058] In summary, this invention provides a catalyst capable of oxidizing soot in diesel engine exhaust gas at relatively low temperatures within the exhaust gas temperature range. This is mainly achieved by controlling the type and content of the complexing agent to convert NO into adsorbed NO2, thereby efficiently oxidizing soot. X With the assistance of [the catalyst], the oxidation of adsorbed NO2 soot formed on the catalyst surface is promoted. The catalyst prepared by the method of this invention exhibits even stronger activity in oxidizing soot than that of precious metals. Moreover, this catalyst possesses excellent water and sulfur resistance as well as cycle stability, indicating that it can operate stably under complex conditions. Furthermore, the synthesis method is easy to operate and simple, possessing great potential for practical application.
[0059] This invention enables accelerated catalytic combustion of soot at low temperatures, maintaining essentially unchanged activity even under complex conditions involving both water vapor and sulfur dioxide. The method is simple to operate, does not use precious metals, and has a very low catalyst production cost. Adding a complexing agent containing alkali metals affects the lattice oxygen mobility of the lanthanum-based perovskite catalyst, as well as the types and conversion processes of intermediate nitrogen oxides adsorbed on the catalyst surface. This catalyst first effectively converts NO into monodentate nitrite, and then further into adsorbed NO2, thus oxidizing soot more efficiently. This simple method of adding a complexing agent containing alkali metals regulates the catalyst's redox capacity and the amount of NO adsorbed on the surface. x type.
[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. The application of a perovskite catalyst in the catalytic oxidation of soot in diesel vehicle exhaust, characterized in that, The preparation method of perovskite catalysts includes the following steps: (1) Add metal ions to the deionized aqueous solution of the chelating agent; the metal ions are a mixture of lanthanum metal ions and transition metal ions; then add citric acid and stir until a clear solution is obtained; the chelating agent is disodium ethylenediaminetetraacetate; the molar ratio of the chelating agent to the metal ions is y, y = 0.1; the transition metal source is one of cobalt nitrate hexahydrate, manganese nitrate hexahydrate, and copper nitrate trihydrate; (2) Gradually add ammonia solution to the mixture prepared in step (1) to adjust the pH value; (3) After evaporating the water from the mixture obtained in step (2), the mixture is calcined at high temperature to obtain the perovskite catalyst.
2. The application according to claim 1, characterized in that, The molar ratio of citric acid to metal ions is x, where 1 ≤ x ≤ 1.
2.
3. The application according to claim 1, characterized in that, In step (2), the pH value is 6.5-7.
5.
4. The application according to claim 1, characterized in that, In step (3), the high-temperature calcination conditions are calcination at 300-400℃ for 1-2 hours and calcination at 600-800℃ for 5-6 hours.
5. The application according to claim 1, characterized in that, In step (3), the high-temperature calcination conditions are calcination at 350℃ for 1-2 hours and calcination at 700℃ for 5-6 hours.