Preparation and application of a transition metal-supported perovskite catalyst

Abstract

The present invention discloses a method for preparing a catalyst having a plasma resonance effect transition metal loaded on an ABO3 type mixed metal oxide perovskite as a carrier and its application in the field of photothermal catalytic methane dry reforming. The catalyst is a catalyst M@ABO3 prepared by loading M metal ions M on an ABO3 type perovskite, wherein A is a lanthanide metal element, B is a transition metal element, and M is a transition metal with a plasma resonance effect of the VIII group. The catalyst of the present invention can effectively reduce the energy barrier of the methane dry reforming reaction under the synergy of light and heat by coupling the high efficiency of thermal catalysis with the low energy consumption of photocatalysis, promote the activation of methane and carbon dioxide, and then achieve high reaction efficiency, and its synthesis method is simple, the yield is considerable, and the high temperature deactivation of the catalyst can be effectively suppressed, while showing a better performance than pure photocatalysis or thermal catalysis, and has good industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic methane conversion, and specifically relates to a method for preparing a catalyst using ABO3 type mixed metal oxide perovskite as a carrier to load a transition metal with a plasma resonance effect, and its application in the field of photothermal catalytic methane dry reforming. Background Art

[0002] With the increasing exhaustion of fossil fuels, the simplest hydrocarbon, methane (CH4), has gradually come onto the stage of history. CH4 is the world's largest hydrocarbon reserve and is widely found in natural gas, biogas and coal mines. In addition, CH4 can be naturally generated from biological systems or produced from biomass through biotechnology, and is an important part of today's energy market. The combustion products of CH4 are only carbon dioxide and water, which will not further pollute the environment and is a clean energy source. However, both CH4 and CO2 are key gases that cause the greenhouse effect. At present, the commonly used method is to use reforming reactions to convert CH4 and CO2 into synthesis gas (H2+CO), which is then used to synthesize high-value hydrocarbon raw materials. This not only helps alleviate environmental problems such as the greenhouse effect, but also provides important chemical raw materials / fuels to make up for energy shortages.

[0003] Methane reforming refers to the process of using metal catalysts to catalyze the reaction of CH4 and CO2 under high temperature and pressure. During the reaction, CH4 acts as a reducing agent and CO2 acts as an oxidant. However, both CH4 and CO2 are extremely stable molecules in thermodynamics and difficult to activate. Therefore, the CH4 dry reforming reaction generally requires a high temperature of 800-1000 °C to be effective. However, metal catalysts are prone to sintering, deactivation, and carbon deposition in such a harsh environment, which in turn blocks the adsorption of reactant molecules by metal active sites, resulting in catalyst deactivation. In recent years, photothermal catalysis has been proven to effectively promote CH4 dry reforming. Photothermal catalysis combines the high efficiency of thermal catalysis with the low energy consumption of photocatalysis, using ultraviolet, visible and infrared light in solar energy to induce reactions and avoid sintering of metal catalysts. Photothermal catalysis can achieve efficient methane dry reforming under medium and high temperature conditions. Based on the above research background, it is obviously of great research significance and practical value to develop efficient photocatalysts and use photothermal catalysis technology to achieve efficient conversion of CH4 and CO2.

[0004] Traditional metal oxide semiconductor catalysts, such as TiO2, Ga2O3, ZrO2, etc., often have disadvantages such as low quantum efficiency, poor light absorption performance, and poor structural stability, which seriously limit the photocatalytic efficiency. ABO3 type perovskite has excellent thermochemical stability and adjustable catalytic performance, and is a very promising catalytic material. The catalytic activity of perovskite can be regulated by partial substitution of cations at the A and / or B positions, and the B component can stabilize unusual oxidation states, thereby leading to structural defects and obtaining more oxygen vacancy active sites. In view of the above problems, the present invention uses perovskite-type mixed metal oxides (ABO3) to prepare a supported catalyst with high activity, high selectivity and high stability. At the same time, by loading Group VIII metal nanoparticles with plasma resonance effect, light energy is efficiently converted into excited state carriers and heat, and catalytic active sites for the reaction are provided, promoting the activation of CH4 and CO2, and achieving high reaction efficiency. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a catalyst that can be used for photothermal catalytic methane dry reforming and its application. The M@ABO3 perovskite catalyst provided by the present invention can effectively reduce the energy barrier of the methane dry reforming reaction under the condition of photothermal synergy, promote the activation of methane and carbon dioxide, and achieve high reaction efficiency. At the same time, the Group VIII metal nanoparticles with plasma resonance effect can effectively inhibit the high-temperature deactivation of the catalyst, thereby solving the shortcomings of traditional metal oxide catalysts such as low quantum efficiency, poor light absorption performance, and poor structural stability. At the same time, the supported catalyst synthesis method is simple, the yield is considerable, and it has good industrial application prospects.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A transition metal-loaded ABO3 perovskite catalyst is prepared by loading a metal ion M as a co-catalyst on an ABO3 perovskite to obtain a catalyst M@ABO3; wherein A is a lanthanide metal element, B is a transition metal element, and M is a transition metal of group VIII having a plasma resonance effect. The preparation method thereof comprises the following steps:

[0008] 1) Mix a certain proportion of metal nitrate A(NO3)3·xH2O and B(NO3) 2～3 xH2O is dissolved in a certain amount of deionized water to obtain a mixed solution;

[0009] 2) adding an appropriate amount of citric acid to the mixed solution obtained in step 1), and adjusting the pH to neutral with aqueous ammonia;

[0010] 3) placing the mixed solution obtained in step 2) in a water bath, stirring and heating, to form a sol-like product;

[0011] 4) aging the sol-like product obtained in step 3), and then calcining it at high temperature in air;

[0012] 5) The product obtained in step 4) is washed, dried, ground and sieved to obtain ABO3 type perovskite as a catalyst carrier, with a size of 50 to 100 meshes.

[0013] 6) Adding the ABO3 type perovskite obtained in step 5) into the MCl·xH2O solution, fully stirring, impregnating, and reducing to obtain the catalyst M@ABO3.

[0014] Furthermore, the A(NO3)3·xH2O and B(NO3) used in step 1) 2～3 The molar ratio of A(NO3)3·xH2O and B(NO3) is 1:1. 2～3 ·xH2O includes but is not limited to a nitrate. Optimally, the A(NO3)3·xH2O is La(NO3)3·6H2O, and B is Fe(NO3)3·9H2O or Mn(NO3)2·4H2O.

[0015] Further, the amount of citric acid added in step 2) is 1 to 3 times the total molar amount of the metal nitrate used in step 1). Optimally, the ratio of the molar amount of citric acid added to the total molar amount of the metal nitrate is 1:1.

[0016] Further, in step 3), the temperature of the water bath is 60-130°C, and the stirring rate is 100-600 rpm. Optimally, the temperature of the water bath is 70°C, and the stirring rate is 400 rpm.

[0017] Furthermore, in step 4), the aging temperature is 80-160°C for 12 h; the calcination temperature is 300-1000°C, and the heating rate is 3-20°C·min -1 , the time is 4 h. Optimally, the aging temperature is 120 ℃, the calcination temperature is 600 ℃, and the heating rate is 5 ℃·min -1 .

[0018] Furthermore, the solvent used for cleaning in step 5) is deionized water; and the drying method is vacuum drying.

[0019] Furthermore, in step 6), the method of loading the metal M includes but is not limited to photodeposition, sodium borohydride reduction, and hydrogen reduction, and the sodium borohydride reduction is optimized.

[0020] Furthermore, the loading amount of M in the obtained catalyst M@ABO3 is 0.5wt%~2wt%, preferably 1wt%.

[0021] CH4 can be activated on nano-metal particles with plasma resonance effect, and CO2 can be activated on oxygen vacancies of perovskite-type mixed metal oxides, thereby finally generating CO and H2. Therefore, the catalyst M@ABO3 obtained by the present invention can be used for photothermal catalytic dry reforming reaction of methane. Specifically, without using an external heat source, a xenon lamp is used as a light source to fully contact the catalyst M@ABO3 with methane and carbon dioxide to carry out the dry reforming reaction of methane; the reaction temperature is 365-555 °C, and is optimized to be 500 °C.

[0022] The beneficial effects of the technical solution of the present invention are:

[0023] (1) The present invention loads transition metal nanoparticles M on the perovskite-type mixed metal oxide ABO3, which can effectively reduce the energy barrier of methane dry reforming and promote the activation of CH4 and CO2.

[0024] (2) The present invention utilizes Group VIII metal nanoparticles loaded with LSPR effect to inhibit the high temperature deactivation of the catalyst, thereby solving the shortcomings of traditional metal oxide catalysts such as poor light absorption performance and poor structural stability.

[0025] (3) The present invention is simple and easy to implement, and can realize an effective methane dry reforming process without an external heat source, which is conducive to popularization and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD patterns of LFO, 1wt% Ru@LFO, LMO, 1wt% Ru@LMO, LMFO, and 1wt% Ru@LMFO prepared in the examples.

[0027] Figure 2 This is an activity comparison chart of LFO, 1wt% Ru@LFO, LMO, 1wt% Ru@LMO, LMFO, and 1wt% Ru@LMFO catalysts prepared in the examples.

[0028] Figure 3 This is an activity comparison chart of Ru@LMFO catalysts with different loading amounts (0wt%~2wt%).

[0029] Figure 4 XRD patterns of 1wt% Ru@LMFO catalyst before and after photothermal catalytic methane dry reforming.

[0030] Figure 5 This is a comparison chart of the activity of 1wt% Ru@LMFO catalyst in photothermal catalysis and thermal catalysis at the same temperature in a fixed bed reactor.

[0031] Figure 6This is a comparison of the activation energies of photothermal catalysis and thermal catalysis of 1wt% Ru@LMFO catalyst in a fixed bed reactor.

[0032] Figure 7 This is a diagram showing the activity of 1wt% Ru@LMFO catalyst under long-term illumination in a fixed bed reactor. DETAILED DESCRIPTION

[0033] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0034] Example 1 Preparation of perovskite-type mixed oxide ABO3

[0035] Dissolve 2.17 g La(NO3)3·6H2O and 2.02 g Fe(NO3)3·9H2O in 10 mL deionized water. After fully dissolved, add 4 g anhydrous citric acid and adjust the pH to neutral with ammonia water. Place the resulting mixed solution in a 70 ℃ water bath and stir and heat at 400 rpm until a sol-like product is formed. Then, age the resulting sol-like product at 120 ℃ for 12 h and calcine it at 600 ℃ in air atmosphere for 4 h at a heating rate of 5 ℃·min -1 The obtained sample was washed with deionized water, vacuum dried, ground and sieved to obtain LaFeO3 (LFO).

[0036] Replace Fe(NO3)3·9H2O with Mn(NO3)2·4H2O in equal molar amount or part of the molar amount (40%) to obtain LaMnO3 (LMO) and LaFe 0.6 Mn 0.4 O3 (LMFO).

[0037] Example 2 Preparation of M@ABO3 perovskite catalyst

[0038] 100 mg of ABO3 obtained in Example 1 was dispersed in 50 mL of deionized water, and then 0.1 mL of 10 mg / mL RuCl3·3H2O solution was added. After thorough mixing, the mixture was stirred for 5 h, and then a sufficient amount of sodium borohydride solution was added dropwise to make Ru 3+ The ions were reduced and loaded onto the ABO3 carrier, and the resulting precipitate was washed and dried to obtain the M@ABO3 catalyst with a loading of 1 wt%.

[0039] Example 3 Evaluation of the photothermal catalytic methane dry reforming activity of M@ABO3 perovskite catalyst

[0040] The methane dry reforming efficiency evaluation experiment of the M@ABO3 catalyst obtained in Example 2 was carried out in a quartz reactor. The experimental process is as follows: the catalyst is placed in the reactor, the raw gas of CH4 / CO2=1:1 (v / v) is filled, the air in the reactor is exhausted, and a 300 W xenon lamp is used as the light source for continuous illumination without an external heat source. The gas phase products of the system are qualitatively and quantitatively analyzed by an Agilent7890B gas chromatograph equipped with a nickel converter.

[0041] Figure 1 XRD patterns of the prepared LFO, 1wt% Ru@LFO, LMO, 1wt% Ru@LMO, LMFO, and 1wt% Ru@LMFO. Figure 1 It can be seen that the XRD spectrum of the Ru@ABO3 supported catalyst contains all the characteristic peaks of ABO3, and the characteristic peaks of Ru are not shown in the spectrum, which is mainly due to the very low content of Ru and the small particle size.

[0042] Figure 2 The activity comparison chart of the prepared LFO, 1wt% Ru@LFO, LMO, 1wt% Ru@LMO, LMFO, and 1wt% Ru@LMFO catalysts. Figure 2 It can be seen that compared with pure ABO3, Ru@ABO3 catalyst can significantly improve the efficiency of photothermal catalytic methane dry reforming, and the effect of Ru@LMFO is significantly better than that of Ru@LFO and Ru@LMO.

[0043] Example 4 Industrial simulation application of M@ABO3 perovskite catalyst

[0044] The quartz reaction tube filled with 50 mg Ru@LMFO catalyst was placed in a fixed bed reactor and continuously charged with CH4 / CO2 = 1:1 (v / v) feed gas at a flow rate of 50 mL min -1 , space velocity is 60000 mL·g -1 ·h -1 In the absence of an external heating source, a 300 W xenon lamp was used as the light source for continuous illumination.

[0045] Figure 3 The activity comparison of Ru@LMFO catalysts with different loadings (0wt% to 2wt%) in a fixed bed reactor. Figure 3 It can be seen that the Ru@LMFO catalyst with a Ru loading of 1wt% has the best catalytic activity.

[0046] Figure 4The XRD patterns of Ru@LMFO catalyst before and after photothermal catalytic methane dry reforming. As can be seen from the figure, the supported catalyst did not undergo significant changes after the reaction, and no impurity peaks appeared, indicating that it has excellent thermal stability.

[0047] Figure 5 This is a comparison of the activity of Ru@LMFO catalyst in photothermal catalysis and thermal catalysis at the same temperature in a fixed bed reactor. As can be seen from the figure, at the same temperature, the efficiency of Ru@LMFO photothermal catalysis is 1~1.5 times that of thermal catalysis, indicating that the process is a photothermal synergistic process.

[0048] Figure 6 This is a comparison of the activation energy of photothermal catalysis and thermal catalysis of Ru@LMFO catalyst in a fixed bed reactor. As can be seen from the figure, the activation energy value in the thermal catalytic process is 1.5 times that of photothermal catalysis, indicating that the introduction of light effectively reduces the activation energy barrier required for the reaction.

[0049] Figure 7 The figure shows the activity of the Ru@LMFO catalyst under long-term illumination in a fixed bed reactor. As can be seen from the figure, the activity of the Ru@LMFO catalyst can remain almost unchanged within 10 h, indicating that the prepared Ru@LMFO catalyst has excellent photothermal stability.

[0050] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a transition metal-supported ABO3 type perovskite catalyst, characterized in that: The catalyst M@ABO3 is prepared by loading metal ions M on ABO3 type perovskite, wherein A is a lanthanide metal element, B is a transition metal element, and M is a transition metal of group VIII having a plasma resonance effect. ... 1) Mix a certain proportion of metal nitrate A(NO3)3·xH2O and B(NO3) 2～3 xH2O is dissolved in a certain amount of deionized water to obtain a mixed solution; 2) adding an appropriate amount of citric acid to the mixed solution obtained in step 1), and adjusting the pH to neutral with aqueous ammonia; 3) placing the mixed solution obtained in step 2) in a water bath, stirring and heating, to form a sol-like product; 4) aging the sol-like product obtained in step 3) and then calcining it at high temperature in air; 5) washing, drying, grinding and sieving the product of step 4) to obtain ABO3 type perovskite as a catalyst carrier; 6) Adding the ABO3 type perovskite obtained in step 5) into the MCl·xH2O solution, fully stirring, impregnating, and reducing to obtain the catalyst M@ABO3.

2. The method for preparing the transition metal-supported ABO3 type perovskite catalyst according to claim 1, characterized in that: A(NO3)3·xH2O and B(NO3) used in step 1) 2～3 The molar ratio of xH2O is 1:

1.

3. The method for preparing the transition metal-supported ABO3 type perovskite catalyst according to claim 1, characterized in that: The amount of citric acid added in step 2) is 1 to 3 times the total molar amount of the metal nitrate used in step 1).

4. The method for preparing the transition metal-supported ABO3 type perovskite catalyst according to claim 1, characterized in that: In step 3), the temperature of the water bath is 60-130°C, and the stirring speed is 100-600 rpm.

5. The method for preparing the transition metal-supported ABO3 type perovskite catalyst according to claim 1, characterized in that: In step 4), the aging temperature is 80-160°C for 12 h; the calcination temperature is 300-1000°C and the heating rate is 3-20°C·min -1 , time is 4 h.

6. The method for preparing the transition metal-supported ABO3 type perovskite catalyst according to claim 1, characterized in that: The solvent used for cleaning in step (5) is deionized water; and the drying method is vacuum drying.

7. The method for preparing the transition metal-supported ABO3 type perovskite catalyst according to claim 1, characterized in that: The loading amount of M in the obtained catalyst M@ABO3 is 0.5wt%~2wt%.

8. Use of the catalyst prepared by the method of claim 1 in photothermal catalytic methane dry reforming reaction, characterized in that: Without using an external heat source, a xenon lamp is used as a light source to allow the catalyst M@ABO3 to fully contact with methane and carbon dioxide to carry out a dry reforming reaction of methane.

9. The use according to claim 8, characterized in that: The reaction temperature is 365-555°C.

Images