WO2023065400A1

WO2023065400A1 - Porous multi-doped perovskite catalyst and preparation method therefor

Info

Publication number: WO2023065400A1
Application number: PCT/CN2021/128131
Authority: WO
Inventors: 徐慢; 王颖; 朱丽; 王树林; 汪炜; 王恒
Original assignee: 武汉工程大学
Priority date: 2021-10-22
Filing date: 2021-11-02
Publication date: 2023-04-27
Also published as: CN113996310A; CN113996310B

Abstract

Provided are a porous multi-doped perovskite catalyst and a preparation method therefor. The method comprises the following steps: S1: weighing nitrates of various elements according to a stoichiometric ratio La_1.5W_1.5MnMNO_9- _δ as raw materials, dissolving the raw materials in a container, adding a complexing agent to the container, stirring at room temperature for a period of time, and evaporating at a constant temperature for a period of time to obtain a precursor sol; S2: soaking carbon foam in the precursor sol in the container for a period of time, then removing the carbon foam, and drying and calcining same, to obtain a perovskite catalyst having a carbon skeleton; S3: placing the perovskite catalyst having the carbon skeleton in a pure oxygen atmosphere to burn away the carbon skeleton, obtaining a porous triple-doped perovskite catalyst. The prepared catalyst has relatively high physical and mechanical properties, as well as relatively high chemical purity, high specific surface area, a stable structure, and excellent catalytic performance.

Description

A kind of porous multi-doped perovskite catalyst and preparation method thereof

technical field

The invention relates to the technical field of catalysts, in particular to a porous multi-doped perovskite catalyst and a preparation method thereof.

Background technique

At present, the preparation of perovskite catalysts mainly includes coprecipitation method, citric acid sol-gel method, combustion synthesis method, mechanochemical synthesis method, and so on. Among them, the co-precipitation method has a larger specific surface area than other methods, but its crystallinity is low. In addition, its final product will produce a large amount of salts and washing water in addition to being easily polluted by alkali metals, causing great harm to the environment. burden. The citric acid sol-gel method has high crystallinity and is the most effective way to manufacture catalysts with high specific surface area while retaining the most lattice oxygen species. The combustion synthesis method is especially suitable for the production of nanoscale catalyst particles, but due to the complexity of the combustion synthesis process involving multiple endothermic and exothermic reactions, the reaction process is uncontrollable, and the perovskite catalyst material produced by high-temperature calcination is very easy to cause The segregation and recrystallization of the material phase of catalyst particles, the particle size is not uniform, and the catalytic performance fluctuates greatly, which limits the application and development of perovskite catalyst materials. The mechanical shock in the mechanochemical synthesis method can reduce the crystallite size of the precursor to the nanoscale, which allows to obtain the pure perovskite phase at room temperature without heat treatment, and has high stability, but its The obvious disadvantage is that the surface area is too small, and the catalytic activity cannot be exerted.

Contents of the invention

The object of the present invention is to propose a porous multi-doped perovskite catalyst with high specific surface area, stable structure and excellent catalytic performance and a preparation method thereof for the above-mentioned deficiencies in the prior art.

A kind of preparation method of porous multi-doped perovskite catalyst of the present invention comprises the following steps:

S1: According to the La _1.5 W _1.5 MnMNO _9-δ stoichiometric ratio, weigh the nitrates of various elements as raw materials, dissolve the above raw materials in the container, add complexing agent to the container, stir at room temperature for a period of time, and evaporate at constant temperature for a period of time Time to get the precursor sol;

S2: After impregnating the carbon foam into the precursor sol of the container for a period of time, the carbon foam is taken out and dried, and calcined to obtain a carbon-containing skeleton-containing perovskite catalyst;

S3: Put the perovskite catalyst with the carbon skeleton into a pure oxygen atmosphere to burn off the carbon skeleton to obtain the porous triple doped perovskite catalyst.

Further, the W element is one of the alkali/alkaline earth metal elements, the M element is one of the transition metal elements, and the N element is one of the metal ion elements.

Further, in step S1, the specific operation of constant temperature stirring is as follows: the container is placed in a constant temperature water bath at 80°C, magnetically stirred at constant temperature, the rotation speed is 200-500r/min, stirring and evaporating for about 3-10h.

Further, in step S2, the carbon foam is obtained by cutting the foam into pieces and calcining in an inert gas atmosphere for a period of time.

Further, the foam is cut into pieces and placed in a tube furnace, passed through N ₂ , and heated to 500-1000°C for calcination to obtain carbon foam. The temperature increase rate of the tube furnace is 3-10°C/min.

Further, in step S2, the drying temperature is 100-150° C.; the calcination condition is: nitrogen atmosphere, the calcination temperature is 1200-1400° C., and the heating rate is 3-10° C./min.

Further, in step S3, the firing temperature for burning off the carbon skeleton is 500-800° C., and the heating rate is 3-10° C./min.

A porous multi-doped perovskite catalyst is prepared by the above-mentioned preparation method.

The preparation method of the present invention uses a variety of cations for synergistic doping, and changes the lattice structure by adjusting the ion species, causing the lattice to be distorted. The cubic axis (C axis) of the cubic perovskite structure formed by the triple doping increases 3 times, the structure increases more active sites by stacking three single perovskite blocks and the synergistic doping of A and B sites, improves the mobility of oxygen, and generates flowing oxygen at the same time, reducing the carbon area on the surface of the catalyst, making the sample A great catalytic synergistic effect is obtained, and the unique three-dimensional framework of carbon foam is used to shape the catalyst, and the extremely high hydrophilicity of carbon foam is used to absorb and calcinate the precursor to obtain the special opening of the foam. The porous perovskite catalyst with a three-dimensional network skeleton structure reduces the polycondensation and aggregation effects of the precursors prepared by the sol-gel method during the drying and calcination process, thereby preparing a network with high specific surface area and high stability. porous perovskite catalysts.

Multiple doping distorts the lattice structure, some of the metal ions enter the crystal structure, causing more active sites in the lattice, and the other part of the metal ions dissociate on the surface of the lattice to maintain structural stability and charge balance. Doping makes cations enter the crystal structure, and the lattice distortion is aggravated, thereby generating more oxygen vacancies, which greatly improves the catalytic activity of the sample. Due to the good hydrophilicity of carbon foam and the unique three-dimensional network structure, not only can the precursor The body sol is firmly combined with the carbon foam, and has quite excellent structural properties, thereby obtaining a perovskite catalyst with high strength, high porosity, and high stability.

The catalyst prepared by the invention has higher physical and mechanical properties, higher chemical purity, high specific surface area, stable structure and excellent catalytic performance.

Description of drawings

Fig. 1 is the SEM figure of the catalyst prepared by embodiment 1;

2 is a SEM image of the catalyst prepared in Comparative Example 1.

Detailed ways

The following are specific embodiments of the present invention and in conjunction with the accompanying drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

Example 1

(1) According to the La _1.5 Sr _1.5 MnCoNiO _9-δ stoichiometric ratio, weigh the nitrate and manganese nitrate solutions of various metal elements as raw materials, and pour them into a beaker.

(2) Use a pipette to take 15ml of water into a beaker and stir until the solids are completely dissolved.

(3) Weigh the complexing agent citric acid monohydrate, pour it into the solution (2), and stir for 10 minutes.

(4) Place the beaker in a constant temperature water bath at 80°C, stir and evaporate for about 3 hours.

(5) Cut the foam into pieces, put it into a tube furnace, pass N ₂ , and raise the temperature to 700° C. to obtain carbon foam. The heating rate of the tube furnace is 5° C./min.

(6) Soak the carbon foam obtained above into the beaker described in (4), and then put it into a constant temperature drying oven for drying, and the drying temperature is 100°C.

(7) Put the dried carbon foam obtained above into a muffle furnace for calcination in a nitrogen atmosphere to obtain a perovskite catalyst containing a carbon skeleton. The calcination temperature is 1200° C., and the heating rate is 10° C./min.

(8) Put the carbon-skeleton-containing catalyst obtained above into a pure oxygen atmosphere to burn off the carbon skeleton to obtain the porous triple-doped perovskite. The firing temperature for burning off the carbon skeleton is 800° C., and the heating rate is 5 °C/min.

According to the above scheme, the chemical formula of the doped catalyst is La _1.5 Sr _1.5 MnCoNiO _9-δ , as shown in Figure 1, under the scanning electron microscope, it can be observed that the structure of the catalyst is a three-dimensional network structure with uniform phase formation and pore size Similar, the skeleton is complete, and the catalytic activity is high. In this example, the partial substitution of La by Sr leads to the appearance of Mn ⁴⁺ and more oxygen vacancies, which improves the catalytic activity and provides more adsorption sites and A-site defects, which can be achieved by providing more active oxygen and Exposure of more manganese ions in the cell improves the oxidation capacity of the catalyst. The doping of Co is beneficial to improve the catalytic activity of Sr doping, and the synergistic effect of A and B positions increases the lattice defects and generates more active sites. The triple doped perovskite catalyst is more active than the single doped perovskite The catalyst showed a higher conversion rate when catalyzing the combustion of methane, and at the same time, the strong interaction between dopant ions and original ions lowered the combustion temperature during methane oxidation, showing better catalytic activity.

Example 2

Change the calcination temperature of step (7) in Example 1 to 1400°C, the firing temperature of the carbon foam in step (5) is 600°C, and the Ni doping element in La _1.5 Sr _1.5 MnCoNiO _9-δ is replaced by Cu, other processing parameters are identical with embodiment 1.

Specific steps are as follows:

(1) According to La _1.5 Sr _1.5 MnCoCuO _9-δ stoichiometric ratio, weigh the nitrate and manganese nitrate solutions of various metal elements as raw materials, and pour them into a beaker.

(5) Cut the foam into pieces, put it into a tube furnace, pass N ₂ , and raise the temperature to 600° C. to obtain carbon foam. The heating rate of the tube furnace is 5° C./min.

(7) Put the dried carbon foam obtained above into a muffle furnace for calcination in a nitrogen atmosphere to obtain a perovskite catalyst containing a carbon skeleton. The calcination temperature is 1400° C. and the heating rate is 10° C./min.

According to the above scheme, the chemical composition of the doped catalyst is La _1.5 Sr _1.5 MnCoCuO _9-δ . Under the scanning electron microscope, it can be observed that the catalyst has a three-dimensional network structure, with relatively loose pore size, close size distribution and complete skeleton. After analysis, the replacement of transition metals does not affect the overall structure of the catalyst, and the catalytic activity is equivalent.

Example 3

Change the calcining temperature of step (7) in Example 1 to 1300°C, the firing temperature of the carbon foam in step (5) is 800°C, and the Sr doping element in La _1.5 Sr _1.5 MnCoNiO _9-δ is replaced by B, other processing parameters are identical with embodiment 1.

Specific steps are as follows:

(1) According to the La _1.5 Ba _1.5 MnCoNiO _9-δ stoichiometric ratio, weigh the nitrate and manganese nitrate solutions of various metal elements as raw materials, and pour them into a beaker.

(5) Cut the foam into pieces, put it into a tube furnace, pass N ₂ , and raise the temperature to 800° C. to obtain carbon foam. The heating rate of the tube furnace is 5° C./min.

(7) Put the dried carbon foam obtained above into a muffle furnace for calcination in a nitrogen atmosphere to obtain a perovskite catalyst containing a carbon skeleton. The calcination temperature is 1300° C. and the heating rate is 10° C./min.

According to the above scheme, the chemical composition of the doped catalyst is La _1.5 Ba _1.5 MnCoNiO _9-δ . Under the scanning electron microscope, it can be observed that the structure of the catalyst is approximately a three-dimensional network structure with a slightly larger pore size and a loose and porous structure. After analysis, the replacement of alkaline earth metals does not affect the overall structure of the catalyst, and the catalytic activity is not much different.

Comparative example 1

After the step (4) of the embodiment, proceed as follows:

The beaker was placed in an electric constant temperature blast drying oven, and kept dry for 10 hours.

The precursor obtained above was transferred to a crucible, put into a muffle furnace, heated to 700° C. under air, kept for 3 hours, and cooled naturally to obtain a black powdery solid.

Other processing parameters are identical with embodiment 1.

According to the above scheme, the chemical formula of the doped catalyst is La _1.5 Sr _1.5 MnCoN _i O _9-δ , as shown in Figure 2, the catalyst can be observed under a scanning electron microscope as powdery, disordered nanoparticles. The high dispersion of nickel enhances the activity, and the addition of a third metal in the perovskite lattice increases the lattice defects, thereby generating mobile oxygen and helping to reduce the surface coking of the catalyst. However, the prepared catalyst is in an amorphous form, and compared with Example 1, the specific surface area is too small, and the contact area with the catalyzed substance is too small. At the same time, the comparative example has poor trapping performance for soot, and its catalytic oxidation performance is not as good as that of Example. 1.

Comparative example 2

According to the La _1.5 Sr _1.5 Mn ₃ O _9-δ stoichiometric ratio, the nitrate and manganese nitrate solutions of various elements of the raw materials were weighed, and other steps and process parameters were the same as in Example 1.

According to the above scheme, the chemical composition of the doped catalyst is La _1.5 Sr _1.5 Mn ₃ O _9-δ , and it can be observed under a scanning electron microscope that the catalyst is powdery and disordered nanoparticles. Although the partial doping of Sr replacing La improves the catalytic activity to a certain extent, but the catalytic ability is not strong due to the limited concentration of substituting ions and the small lattice distortion. Meanwhile, the specific surface area of Comparative Example 2 is much smaller than that of Example 1, and the soot trapping performance is poor, so the catalytic oxidation performance of this Comparative Example is not as good as that of Example 1.

Comparative example 3

(1) According to La _1.5 Sr _1.5 Mn ₂ CoO _9-δ stoichiometric ratio, the nitrate and manganese nitrate solutions of various metal elements as raw materials were weighed, and other steps and process parameters were the same as in Example 1.

According to the above scheme, the chemical composition of the doped catalyst is La _1.5 Sr _1.5 Mn ₂ CoO _9-δ , and it can be observed under a scanning electron microscope that the catalyst is powdery and disordered nanoparticles. The partial doping of Sr instead of La, on the one hand, causes lattice distortion, and on the other hand, the doping of Co improves the catalytic activity of Sr, but because the concentration of Mn elements replaced is limited, therefore, compared with triple doping, two The catalytic activity of heavy doping is relatively weak. Simultaneously, the physical factor that influences catalytic activity is exactly specific surface area, and the specific surface area of this comparative example 3 is far smaller than embodiment 1, therefore, cause its catalytic performance and soot trapping capacity not as good as embodiment because of the double reason of its chemical composition and physical structure 1.

What is not involved above is applicable to the prior art.

Although some specific embodiments of the present invention have been described in detail by examples, those skilled in the art should understand that the above examples are only for illustration, rather than for limiting the scope of the present invention. Various modifications or additions or similar substitutions can be made to the described specific embodiments without departing from the direction of the present invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above implementations based on the technical essence of the present invention shall be included in the protection scope of the present invention.

Claims

A method for preparing a porous multi-doped perovskite catalyst, characterized in that: comprising the steps of:

S1: According to the La 1.5 W 1.5 MnMNO 9-δ stoichiometric ratio, weigh the nitrates of various elements as raw materials, dissolve the above raw materials in the container, add complexing agent to the container, stir at room temperature for a period of time, and evaporate at constant temperature for a period of time Time to get the precursor sol;

S2: After impregnating the carbon foam into the precursor sol in the container for a period of time, the carbon foam is taken out and dried and then calcined to obtain a carbon-containing perovskite catalyst;

S3: Put the perovskite catalyst with the carbon skeleton into a pure oxygen atmosphere to burn off the carbon skeleton to obtain the porous triple doped perovskite catalyst.
The preparation method of a kind of porous multi-doped perovskite catalyst as claimed in claim 1, is characterized in that: W element is a kind of in alkali/alkaline earth metal element, M element is a kind of in transition metal element, The N element is one of metal ion elements.
The preparation method of a porous multi-doped perovskite catalyst according to claim 1, characterized in that: in step S1, the specific operation of constant temperature stirring is that the container is placed in a constant temperature water bath at 80°C, and the constant temperature magnetic stirring is performed at a speed of 200-500r/min, stirring and evaporating for about 3-10h.
The preparation method of a porous multi-doped perovskite catalyst according to claim 1, characterized in that: in step S2, the carbon foam is calcined in an inert gas atmosphere for a period after the foam is cut into pieces get after time.
The preparation method of a porous multi-doped perovskite catalyst according to claim 2, characterized in that: the foam is cut into pieces and placed in a tube furnace, passed through N 2 , heated to 500-1000°C and calcined to obtain For carbon foam, the heating rate of the tube furnace is 3-10°C/min.
The preparation method of a porous multi-doped perovskite catalyst according to claim 1, characterized in that: in step S2, the drying temperature is 100-150°C.
The preparation method of a porous multi-doped perovskite catalyst as claimed in claim 6, characterized in that: the calcination conditions are: nitrogen atmosphere, the calcination temperature is 1200-1400°C, and the heating rate is 3-10°C/min .
The preparation method of a porous multi-doped perovskite catalyst according to claim 1, characterized in that: in step S3, the firing temperature for burning off the carbon skeleton is 500-800°C, and the heating rate is 3-10 °C/min.
A porous multi-doped perovskite catalyst, characterized in that it is prepared by the preparation method described in any one of claims 1-8.