阅读说明：本技术 一种多级分层结构铁镍合金催化剂的制备方法及应用 (Preparation method and application of iron-nickel alloy catalyst with multi-stage layered structure ) 是由 窦立广 闫存极 李鑫 肖立业 王磊 马天增 于 2019-09-30 设计创作，主要内容包括：一种多级分层结构铁镍合金催化剂的制备方法及应用,使用适量柠檬酸作为螯合剂,结合过量金属盐溶液,通过水热过程和后续的煅烧-还原步骤,制备得到泡沫镍负载尺寸为5～12nm、高分散的整体式FeNi合金催化剂。催化剂底层为交错生长的纳米片阵列,顶层表现为自组装而成的球形纳米粒子,赋予催化剂发达的孔隙结构有助于增强后续的表面催化反应,并提高了泡沫镍基质的电阻率,可用于电热催化过程。本发明催化剂的分层多级结构形貌克服了传统负载型催化剂易从载体表面脱落、分散度差、活性粒子易团聚的缺点,拓宽了泡沫镍材料在电热催化领域中的应用范围。(A preparation method and application of a multi-level layered structure iron-nickel alloy catalyst are disclosed, wherein a proper amount of citric acid is used as a chelating agent, an excessive metal salt solution is combined, and a high-dispersion monolithic FeNi alloy catalyst with a foamed nickel load size of 5-12 nm is prepared through a hydrothermal process and subsequent calcination-reduction steps. The bottom layer of the catalyst is a nano-sheet array which grows in a staggered mode, the top layer of the catalyst is spherical nano-particles formed by self-assembly, a developed pore structure of the catalyst is endowed, the subsequent surface catalytic reaction is enhanced, the resistivity of the foamed nickel matrix is improved, and the catalyst can be used for an electrothermal catalytic process. The layered multi-stage structure morphology of the catalyst overcomes the defects that the traditional supported catalyst is easy to fall off from the surface of the carrier, has poor dispersion degree and is easy to agglomerate active particles, and widens the application range of the foamed nickel material in the field of electrothermal catalysis.)

1. A preparation method of a multi-stage layered structure iron-nickel alloy catalyst is characterized by comprising the following steps: the preparation method of the iron-nickel alloy catalyst with the multi-stage layered structure comprises the following steps:

(1) taking a high-porosity foamed nickel metal substrate as a conductive support framework, respectively placing the conductive support framework in a hydrochloric acid solution, deionized water and absolute ethyl alcohol for ultrasonic treatment, and drying in a vacuum drying oven for 6 hours to obtain a foamed nickel substrate without an oxide layer on the surface;

(2) Dissolving metal salt, urea and citric acid in deionized water at the same time, transferring the solution into a 100ml polytetrafluoroethylene lining, putting the foamed nickel metal substrate in the step (1), sealing the foamed nickel metal substrate, putting the sealed foamed nickel metal substrate in a stainless steel kettle for screwing, putting the sealed foamed nickel metal substrate in a forced air drying box for hydrothermal reaction, standing the sealed foamed nickel metal substrate at room temperature after the reaction is finished, washing the obtained product with the deionized water until the pH value is 7, and drying the product to obtain a LDHs/foamed nickel precursor with a multi-level layered structure;

(3) The precursor obtained in the step (2) is put in H₂Roasting in a reducing atmosphere to obtain a corresponding multistage layered iron-nickel alloy catalyst;

The high-porosity foamed nickel metal substrate in the step (1) is 50-100 mm long, 4-6 mm wide, 1-1.5 mm thick and long: the width is not less than 10:1, the porosity is higher than 95%, the concentration of hydrochloric acid is 3-6 mol/L, the ultrasonic power is 300W, and the ultrasonic time is 0.25-0.5 h;

In the step (2), the metal salt includes divalent Ni²+ and trivalent Fe³+, trivalent Al³+ a metal salt in the form of one or a mixture of nitrates or chlorides, Ni²+ and Fe³+、Al³+ has a molar ratio of [ Ni²+]/[Fe³++Al³+]3: 1, the metal salt and urea are in large excess relative to the nickel metal base foam, every 1mmol of divalent Ni²+ corresponds to 10mg of foamed nickel metal substrate; the hydrothermal temperature is selected to be 110-140 ℃, the time is 8-12 h, the room-temperature standing time is 12h, and the drying condition is the same as that of the step (1), so that the hierarchical LDHs/foam nickel precursor Ni with the multilevel structure is obtained₃Fe_xAl_y-LDHs/NF；

In the step (3), the roasting conditions are as follows: introduction of H₂Roasting the/Ar mixed gas at 500-600 ℃, heating up at a rate of 1-2 ℃/min for 3h to obtain the multi-stage layered Fe-Ni alloy catalyst Ni₃Fe_xAl_y/NF。

2. The method of preparing a multi-stage layered structure iron-nickel alloy catalyst according to claim 1, wherein: in the step (2), Ni²⁺And Fe³⁺、Al³⁺among the molar ratios of [ B ], preferred is [ Fe ]³⁺]/[Al³⁺]0.33 to 1, preferably [ urea ]]/[Ni²⁺+Fe³⁺+Al³⁺]The amount of [ urea ] is preferably 3.33 to 4]/[ citric acid ]]＝10～20。

3. The method of preparing a multi-stage layered structure iron-nickel alloy catalyst according to claim 1, wherein: the LDHs/foam nickel precursor with the multi-stage layered structure is expressed as NiFeAl-LDHs/NF, and is characterized in that LDHs nanosheets are ordered and layered and grow on a foam nickel substrate, wherein the LDHs nanosheets at the bottom layer are mutually staggered to form a nanosheet array, the diameter of the nanosheet is 50-100 nm, and the thickness of the nanosheet is 5-10 nm; the top-layer LDHs nanosheets are mutually self-assembled into a spherical shape, the diameter of the nanosheets is 100-300 nm, the thickness of the nanosheets is 8-12 nm, and the nanosheets are in close contact with the bottom-layer nanosheet array, so that the precursor presents a special layered three-dimensional multilevel structure shape; and roasting the precursor, wherein the obtained alloy catalyst still maintains the morphological characteristics, the catalyst is expressed as NiFeAl/NF, all Fe and Ni form small-size alloy particles, and the size of the alloy particles is 5-10 nm.

4. The method of preparing a multi-stage layered structure iron-nickel alloy catalyst according to claim 1, wherein: connecting two ends of the multistage layered iron-nickel alloy catalyst prepared in the step (3) into a circuit through a pure copper wire, loading current to generate joule heat, and driving a catalytic reaction; the current loading range is between 0A and 6A, the voltage loading range is between 0V and 30V, and the heat production temperature of the catalyst is optimized to be between 150 ℃ and 400 ℃.

5. the method of preparing a multi-stage layered structure iron-nickel alloy catalyst according to claim 1, wherein: the preparation method is used for the electro-thermal catalysis process.

Technical Field

The invention relates to a preparation method and application of a multi-stage layered structure iron-nickel alloy catalyst.

Background

Today, human production activities are free to emit CO₂Greenhouse gases bring about numerous environmental problems, and thus the green and sustainable development of economy is severely restricted. In the treatment of CO in a plurality of ways₂In the technical scheme, CO₂Hydrogenation for preparing CH₄The reaction can be carried out under normal pressure (CO)₂+4H₂→CH₄+2H₂O,ΔG₂₉₈130.8kJ/mol), is also the most direct technical approach for realizing efficient circulation of carbon resources, and has received extensive research attention. However, the high operation temperature (250-450 ℃) of methanation reaction and the hot spot generated in the local strong exothermic process are very easy to deposit carbon on the surface of the catalyst or sinter the traditional Ni active particles, which leads to irreversible inactivation of the catalyst ((F.Song, et al. int.J.hydrogen Energy,2017,42,4174-4183) — based on this, the development of a novel catalytic technology route and the design of a novel structure and a special morphology nano catalyst gradually become the current CO₂Hot spot direction in the hydrogenation field.

Hydrotalcite (LDHs) shows excellent catalytic activity due to its composition adjustability, lattice positioning effect (high dispersion) and intrinsic basicity. In particular, monolithic catalysts prepared by calcining hydrotalcite precursors loaded on porous Nickel Foam (NF) have attracted great research interest in the field of heterogeneous catalysis due to their high thermal conductivity and excellent mass transfer capacity (y.k.li, et al.aiche Journal,2015,61, 4323-4331). Inevitably, however, uneven heating of the catalyst bed in exothermic catalytic reactions results in a large portion of the catalyst being used with reduced efficiency, agglomeration deactivation and high energy consumption during the reaction. In view of this, the university of Denmark science and technology, Chorkendorff and Denmark Town, 2019Mortens et al, Pusuo corporation proposed a scheme for electrically heating a FeCrAl metal tube reactor (S.T. Wismann, et al. science,2019,364,756-759) with CH₄Steam reforming to produce H₂For example, the heating source is in direct close contact with the Ni catalytic sites during the reaction, which can greatly improve the uniformity of heating. However, since the nickel foam has high conductivity, the conventional LDHs loading method (solvothermal method or electrodeposition) does not substantially increase the resistivity of the whole material although many methods are reported, and thus the method is still frequently used for supercapacitors or related electrode materials. Such as Huang, et al. The invention has the following patent: CN 108193227A constructs a nickel-iron hydrotalcite composite structure film on a foamed nickel substrate by an in-situ electrodeposition method, can be used for an electrocatalytic oxygen evolution electrode, and shows excellent electrocatalytic activity. Fan, etc. The invention has the following patent: CN 108554413A prepares the nickel-based electrocatalytic material with the three-dimensional multilevel structure through a hydrothermal method and a subsequent calcination process, and shows excellent electrocatalytic oxygen evolution activity. The surface resistivity of the foam nickel composite material is closely related to the composition, morphology and particle size of a loaded material, however, the current preparation method causes the foam nickel-based composite material to still have high conductivity and is difficult to be used in the resistance thermal catalytic reaction driven by full electricity, and therefore, the resistance thermal application based on the hydrotalcite/foam nickel system derived catalyst is not reported in relevant researches.

Disclosure of Invention

The invention aims to provide a preparation method of a multi-stage layered structure iron-nickel alloy catalyst and application of the catalyst in the field of electro-thermal catalysis. The preparation method is simple and convenient in preparation process, is suitable for batch production, and can avoid the use of a large amount of organic reagents.

The active phase in the multi-stage layered morphology iron-nickel alloy catalyst prepared by the invention is FeNi alloy particles with small size and high dispersion, and the current monolithic catalyst greatly improves the self resistivity of foam Nickel (NF) after crystal grain growth and layered nucleation, can be conveniently used for an electro-thermal catalysis process, and simultaneously shows excellent CO catalysis₂Manufacture of CH₄And (4) activity.

The method directly adopts conventional urea as a precipitator, simultaneously uses a proper amount of citric acid as a chelating agent, prepares a hydrotalcite (LDHs)/foamed nickel precursor with a multi-stage layered morphology through a simple and green hydrothermal process, and calcines the hydrotalcite (LDHs)/foamed nickel precursor at a slow heating rate in a reducing atmosphere to obtain the multi-stage layered iron-nickel alloy catalyst, wherein FeNi alloy particles are kept highly dispersed and ultra-small in size based on the lattice confinement effect of the hydrotalcite (LDHs). Meanwhile, the monolithic catalyst prepared by the invention shows a developed pore structure, and is beneficial to enhancing the surface catalytic reaction. In particular, based on the layered morphology of the catalyst, compared with the traditional foamed nickel, the resistivity of the obtained monolithic catalyst is obviously increased, and the monolithic catalyst can be used as a monolithic resistor and can perform self-heating through externally applied current, so that the invention can be used in resistance thermocatalytic reaction. Compared with the existing electrothermal catalyst, the catalyst prepared by the invention has the advantages that the proportion of the active center Fe and the active center Ni is adjustable, and the characteristics of small size and high dispersion are kept. Meanwhile, the nano layer is stably attached to the foamed nickel metal substrate due to the strong bonding effect among the nano particles in the crystallization process, and the powder is not easy to fall off or fall off in the reaction process, so that the integral electrothermal alloy type catalyst with stable current structure and morphology is obtained.

The precursor of the multi-stage layered FeNi alloy catalyst is expressed as NiFeAl-LDHs/NF, and is characterized in that LDHs nanosheets are ordered and layered and grow on a foamed nickel substrate, wherein the LDHs nanosheets at the bottom layer are mutually staggered to form a nanosheet array, the diameter of the nanosheet is 50-100 nm, and the thickness of the nanosheet is 5-10 nm; the top LDHs nanosheets are mutually self-assembled into a spherical shape, the diameter of the nanosheets is 100-300 nm, the thickness of the nanosheets is 8-12 nm, and the nanosheets are in close contact with the bottom nanosheet array, so that the precursor presents a special layered three-dimensional multilevel structural shape. And (2) moderately roasting the precursor, wherein the obtained alloy catalyst still maintains the morphological characteristics, the catalyst is NiFeAl/NF, has developed pores and high specific surface area, and all Fe and Ni form small-size alloy particles with the size of 5-10 nm. The obtained alloy catalyst needs to be integrally used as a resistor, joule heat is directly generated by adding a proper electric field to act on FeNi alloy particles, and the heterogeneous catalytic reaction is driven.

The preparation method of the iron-nickel alloy catalyst with the multi-stage layered structure comprises the following steps:

(1) Taking a high-porosity foamed nickel metal substrate as a conductive support framework, respectively placing the conductive support framework in a hydrochloric acid solution, deionized water and absolute ethyl alcohol for ultrasonic treatment, and drying in a vacuum drying oven for 6 hours to obtain a foamed nickel substrate without an oxide layer on the surface;

(2) Dissolving metal salt, urea and citric acid in deionized water at the same time, transferring the solution into a 100ml polytetrafluoroethylene lining, putting the foamed nickel metal substrate in the step (1), sealing the foamed nickel metal substrate, putting the sealed foamed nickel metal substrate in a stainless steel kettle for screwing, putting the sealed foamed nickel metal substrate in a forced air drying box for hydrothermal reaction, standing the sealed foamed nickel metal substrate at room temperature after the reaction is finished, washing the obtained product with the deionized water until the pH value is 7, and drying the product to obtain a LDHs/foamed nickel precursor with a multi-level layered structure;

(3) The precursor obtained in the step (2) is put in H₂Roasting in a reducing atmosphere to obtain a corresponding multistage layered iron-nickel alloy catalyst;

the high-porosity foamed nickel metal substrate in the step (1) is 50-100 mm long, 4-6 mm wide, 1-1.5 mm thick and long: the width is not less than 10:1, the porosity is higher than 95%, the concentration of hydrochloric acid is 3-6 mol/L, the ultrasonic power is 300W, and the ultrasonic time is controlled to be 0.25-0.5 h.

In the step (2), the metal salt includes divalent Ni²⁺And trivalent Fe³⁺trivalent Al³⁺A metal salt in the form of nitrate or chloride or their mixture, Ni²⁺And Fe³⁺、Al³⁺Is fixed at a molar ratio of [ Ni ]²⁺]/[Fe³⁺+Al³⁺]3: 1, preferably [ Fe ]³⁺]/[Al³⁺]0.33 to 1, preferably [ urea ]]/[Ni²⁺+Fe³⁺+Al³⁺]The amount of [ urea ] is preferably 3.33 to 4]/[ citric acid ]]5-10. The metal salt and urea are in large excess relative to the nickel metal base foam, every 1mmol of bivalent Ni²⁺Corresponding to 10mg of a foamed nickel metal substrate. The hydrothermal temperature is selected to be 110-140 ℃, the time is 8-12 h, the room-temperature standing time is 12h, and the drying condition is the same as that of the step (1), so that the hierarchical LDHs/foam nickel precursor Ni with the multilevel structure is obtained₃Fe_xAl_y-LDHs/NF。

In the step (3), the roasting conditions are as follows: introduction of H₂Roasting the/Ar mixed gas at 500-600 ℃, heating up at a rate of 1-2 ℃/min for 3h to obtain the multi-stage layered Fe-Ni alloy catalyst Ni₃Fe_xAl_y/NF。

And (4) connecting two ends of the modular multistage layered iron-nickel alloy catalyst obtained in the step (3) into a circuit through a pure copper wire, and loading current to generate Joule heat to drive catalytic reaction. The current can be direct current or alternating current, the current loading range is 0A-6A, the voltage loading range is 0V-30V, and the heat production temperature of the catalyst is optimized to be 150-400 ℃.

the preparation process and the principle of the invention are as follows: in the starting solution, the pH of the solution is brought about by the presence of large amounts of metal nitrates<7, the citric acid generates primary and secondary ionization under the acidic condition and is mixed with Fe in the solution³⁺、Ni²⁺、Al³⁺Metal ions are coordinated, so that the metal ions in the solution are captured and gathered around the foam nickel supporting framework; then urea is used as a precipitator, and NH is generated by gradual decomposition in the heating process₃Precipitating the metal ions in the solution to form hydroxide species thereof; at this time, due to the presence of the nickel foam matrix, heterogeneous nucleation of metal ions occurs at the surface thereof based on its porous structure and rough dielectric surface, forming starting crystallites. The existence of citric acid can obviously inhibit the homogeneous nucleation process of metal ions and promote the precipitation nucleation of the metal ions on a supporting framework, and particularly, in the preparation method, after the excessive salt solution forms a primary array on the surface of a foamed nickel matrix, the nucleation continues on the surface of the array, the self-assembly forms a spherical morphology stacked by nano sheets, and strong interaction force exists between the nano layers. During calcination-reduction, by a very slow rate of temperature rise: 1-2 ℃/min, continuously maintaining the multi-stage morphology, simultaneously overflowing Ni and Fe from the LDHs laminate, and H₂And fusing at high temperature in the atmosphere to form small-size alloy particles, and highly dispersing the obtained alloy particles based on the lattice positioning effect of LDHs to obtain the multistage layered iron-nickel alloy catalyst. Due to the layered structure of the catalyst prepared by the invention, the catalystThe catalyst maintains higher resistivity, and can be directly loaded with current to carry out fully electrically driven electro-thermal catalytic reaction.

Compared with the prior art, the invention has the following advantages and characteristics:

(1) the preparation method of the multistage layered FeNi alloy catalyst provided by the invention is not reported in documents, and particularly, the multistage layered FeNi alloy catalyst is obtained by adopting an excess salt solution method for the first time, taking urea as a precipitator and a proper amount of citric acid as a chelating agent through a green hydrothermal method and a subsequent calcination-reduction process.

(2) The NiFeAl/NF prepared by the method has a unique multistage layered morphology, the bottom layer is a nanosheet array, the diameter of the nanosheet is 50-100 nm, the thickness of the nanosheet is 5-10 nm, the top layer is self-assembled spherical particles, the particle size is 100-300 nm, Fe and Ni elements separated out from the laminated plate directly form a bimetal alloy, small-size and high-dispersion characteristics are kept, and the size of the spherical particles is 5-10 nm.

(3) in the electro-thermal catalysis application, the multi-level structure layered catalyst shows obviously improved resistivity, so that the current can be directly loaded to fully electrically drive and catalyze CO₂Hydrogenation breaks through the cognition that the foamed nickel can only be used as a high-conductivity electrode material. The performance test result shows that the catalytic activity of the current FeNi alloy catalyst is improved by 50 percent compared with that of a single Ni particle, the defects of easy falling, low load capacity and easy agglomeration at high temperature of the foam nickel supported catalyst prepared by the traditional method are technically overcome, and the application of the hydrotalcite/foam nickel composite material derived catalyst in the electro-thermal catalysis field is widened.

The preparation method can be used in the field of electro-thermal catalysis.

Drawings

FIG. 1 is a photograph of a real object of LDHs/NF and the catalyst obtained after calcination-reduction; FIG. 1a is a schematic representation of a treated nickel foam; FIG. 1b shows Ni in example 1₃Fe_0.5Al_0.5-LDHs/NF; FIG. 1c shows Ni in example 1₃Fe_0.5Al_0.5/NF; FIG. 1d shows Ni in example 2₃Fe_0.25Al_0.75/NF; FIG. 1e shows Ni in example 3₃Fe_0.33Al_0.66/NF；

FIG. 2 is an SEM electron micrograph of treated nickel foam of examples 1-3;

FIG. 3 is the multi-stage layered Fe-Ni hydrotalcite/Ni foam precursor Ni of example 1₃Fe_0.5Al_0.5SEM micrograph of LDHs/NF;

FIG. 4 shows the multi-stage layered Fe-Ni alloy catalyst Ni of example 1₃Fe_0.5Al_0.5SEM image of/NF bottom layer nano sheet array;

FIG. 5 is the multi-stage layered Fe-Ni alloy catalyst Ni of example 1₃Fe_0.5Al_0.5SEM image of/NF top layer rosette particles;

FIG. 6 is the multi-stage layered Fe-Ni alloy catalyst Ni of example 2₃Fe_0.25Al_0.75SEM picture of/NF;

FIG. 7 shows the multi-stage layered Fe-Ni alloy catalyst Ni of example 3₃Fe_0.33Al_0.66SEM picture of/NF;

FIG. 8 is the multi-stage layered Fe-Ni alloy catalyst Ni of example 3₃Fe_0.33Al_0.66STEM element distribution line scanning diagram of/NF;

FIG. 9 is the multi-stage layered Fe-Ni alloy catalyst Ni of example 3₃Fe_0.33Al_0.66/NF and Ni alone₃Al₁Electro-thermocatalytic CO/NF₂And (5) comparing hydrogenation activities.

Detailed Description