An alloy catalyst, its preparation method and application in catalytic cracking of methane at low temperature

Abstract

The application discloses an alloy catalyst and a preparation method and application thereof in low-temperature catalytic cracking of methane, and belongs to the field of hydrogen production catalysts and preparation technologies thereof. The application solves the problems of low efficiency and high catalytic reaction temperature of the existing methane catalytic cracking. The Ni-Co-In alloy catalyst provided by the application utilizes the alloying among nickel, cobalt and indium, changes the electronic distribution around the metal, and thus increases the catalytic activity of the catalyst. The alloy catalyst contains few types of elements, the proportion among the elements is easy to control, the catalytic activity sites and the catalytic performance of the alloy catalyst for methane cracking are controlled by controlling the proportion of nickel, cobalt and indium in the alloy. 0.65 Co 0.10 In 0.25 The alloy catalyst has a methane conversion rate of 52% at a reaction temperature of 800 DEG C and has good stability within 120 min of reaction.

Description

Technical Field

[0001] This invention relates to an alloy catalyst, its preparation method, and its application in low-temperature catalytic cracking of methane, belonging to the technical field of methane cracking to hydrogen production catalysts and their preparation. Background Technology

[0002] Catalytic methane cracking for hydrogen production is a green, environmentally friendly, efficient, and clean hydrogen production technology. Methane is decomposed at high temperatures to produce hydrogen and solid carbon, without generating carbon oxides. The gaseous product contains only hydrogen and unreacted methane, which can then be further separated using liquefaction or membrane separation technologies to obtain hydrogen with a purity of 99%. Compared to more complex separation processes (removing carbon dioxide or carbon monoxide), this process is simple, consumes less energy, and is environmentally friendly.

[0003] The methane cracking reaction is endothermic, requiring 37.8 kJ / mol of energy to produce hydrogen. The CH bonds in the methane molecule are very stable, requiring relatively high temperatures (above 1200 °C) for complete decomposition. Using a suitable and reliable catalyst can lower the activation energy of the CH bonds, reducing the required reaction temperature. Therefore, selecting and designing a suitable catalyst is crucial.

[0004] Current research on methane cracking for hydrogen production focuses primarily on preparing highly efficient, readily available, inexpensive, and stable catalysts. Among catalysts for methane cracking for hydrogen production, 3d transition metals (Co, Ni, Fe) exhibit significant catalytic activity for the decomposition of hydrocarbons. However, metallic Ni rapidly aggregates and sinters or becomes carbon-coated and deactivated above 600°C, affecting its stability and lifetime. Metallic Fe facilitates the formation of products with specific morphologies and maintains good activity and stability in the 700-1000°C range, but its catalytic activity is lower than that of metallic Ni. Studies have shown that bimetallic / polymetallic catalysts, compared to monometallic catalysts, alter the electron density and geometric properties of the catalyst surface, thus affecting the catalytic reaction pathway, leading to different catalytic mechanisms, and ultimately improving the catalyst's catalytic activity. However, existing bimetallic / polymetallic catalysts generally exhibit high catalytic activity only above 1000°C in the methane cracking reaction; therefore, it is essential to provide a catalyst with high catalytic activity at lower temperatures. Summary of the Invention

[0005] This invention addresses the problems of low efficiency and high reaction temperature in existing methane catalytic cracking processes by providing an alloy catalyst, its preparation method, and its application in low-temperature catalytic cracking of methane.

[0006] The technical solution of this invention:

[0007] One objective of this invention is to provide a method for preparing an alloy catalyst, the method comprising the following steps:

[0008] (1) Oxalic acid solution was added dropwise to a mixed solution containing nickel nitrate, cobalt nitrate and indium nitrate. After the addition was completed, the solution was transferred to a high-pressure reactor for hydrothermal reaction. After the reaction was completed, the precipitate was washed and dried to obtain Ni-Co-In alloy precursor.

[0009] (2) The Ni-Co-In alloy precursor was heat-treated in a CH4-Ar mixed flow atmosphere to obtain the Ni-Co-In alloy catalyst.

[0010] Further specifying, the molar ratio of nickel nitrate, cobalt nitrate and indium nitrate in (1) is 2:1:1 to 5:0:1.

[0011] Further specify that (1) oxalic acid is added in stoichiometric amounts according to the amount required to completely react with nickel nitrate, cobalt nitrate and indium nitrate in the mixed solution.

[0012] Further, in (1), the hydrothermal reaction temperature is 100-200℃ and the time is 10-20h.

[0013] Further specifying, the drying conditions in (1) are: vacuum drying at 40-80℃ for 24-48h.

[0014] Further specified, in (2) the flow rate of the CH4-Ar mixture is 20-80 mL / min, and the volume ratio of CH4 to Ar is 1:1.

[0015] Further specified, (2) the heat treatment temperature is 200~600℃ and the time is 30~90min.

[0016] A second objective of this invention is to provide an alloy catalyst obtained by the above preparation method.

[0017] Furthermore, the aforementioned alloy catalyst is used to catalyze the methane cracking reaction.

[0018] The third objective of this invention is to provide a method for low-temperature catalytic cracking of methane. This method uses the aforementioned alloy catalyst as the cracking reaction catalyst, and the cracking reaction conditions are as follows: under standard atmospheric pressure, the reaction temperature is 700–990 °C, the CH4 gas flow rate is 6–60 mL / min, and the protective gas Ar flow rate is 10–100 mL / min.

[0019] Beneficial effects:

[0020] (1) The Ni-Co-In alloy catalyst provided by this invention utilizes alloying between nickel, cobalt, and indium to alter the electron distribution around the metals, thereby increasing the catalyst's catalytic activity. Furthermore, this alloy catalyst contains few element types, and the elemental ratios are easily controlled. The nickel-cobalt-indium ratio in the alloy can be adjusted by controlling the molar ratio of nickel, cobalt, and indium ions in the precursor, thus achieving regulation of its catalytic active sites and methane cracking catalytic performance. Specifically, this invention obtains a catalyst with high catalytic activity and stability (Ni...) by controlling the ratio of nickel, cobalt, and indium elements. 0.65 Co 0.10 In 0.25 At a reaction temperature of 800℃, its methane conversion rate can reach 52% and it maintains good stability within 120 minutes of reaction.

[0021] (2) The synthesis method of the Ni-Co-In alloy catalyst provided by the present invention is simple, easy to mass-produce, safe to operate, and easy to industrialize.

[0022] (3) The Ni-Co-In alloy catalyst prepared by this invention not only meets the requirements for methane cracking under low-temperature conditions, but also exhibits relatively high conversion rate and stability, maintaining a solid state throughout the reaction temperature range of 700–990°C. Furthermore, at a reaction temperature of 990°C, Ni… 0.65 Co 0.10 In 0.25 The catalyst achieved a methane conversion rate of 91%. Furthermore, the degree of graphitization of the carbon products obtained from the reaction was controllable, especially for Ni. 0.65 Co 0.10 In 0.25 The alloy catalyst exhibits the highest degree of graphitization of carbon products after the catalytic cracking of methane at a reaction temperature of 900℃. This indicates that the alloy catalyst prepared by the method provided in this invention can be regulated differently according to various application scenarios, making it suitable for a wide range of applications. Attached Figure Description

[0023] Figure 1 X-ray powder diffraction patterns of Ni-Co-In alloy catalysts prepared in different embodiments;

[0024] Figure 2 X-ray powder diffraction patterns of Ni-Co-In alloy catalysts prepared in different embodiments after catalyzing methane cracking reaction at 800℃ for 30 min;

[0025] Figure 3 The Ni prepared in Example 4 0.65 Co 0.10 In 0.25 Microscopic morphology images of the alloy catalyst (at different magnifications);

[0026] Figure 4 The Ni prepared in Example 4 0.65 Co 0.10 In 0.25 Microscopic morphology of the alloy catalyst after catalyzing the methane cracking reaction at 800℃ for 30 min (at different magnifications);

[0027] Figure 5 The Ni prepared in Example 4 0.65 Co 0.10 In 0.25 Raman spectra of carbon products after catalytic cracking reaction of alloy catalyst at different temperatures for 30 min;

[0028] Figure 6 The conversion rate of Ni-Co-In alloy catalysts prepared in different embodiments for catalytic methane cracking at a reaction temperature of 800℃;

[0029] Figure 7 The Ni prepared in Example 4 0.65 Co 0.10 In 0.25 The methane conversion rate of the alloy catalyst catalyzing the methane cracking reaction for 10 min at different reaction temperatures;

[0030] Figure 8 The figure shows the stability test results of Ni-Co-In alloy catalysts prepared in different embodiments at a reaction temperature of 800℃. Detailed Implementation

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0033] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, all materials, reagents, methods, and instruments used are conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art. Furthermore, all solid and liquid reagents used are of analytical grade.

[0035] Example 1

[0036] This embodiment synthesizes Ni 0.50 Co 0.25 In 0.25 The process of alloy catalysts is as follows:

[0037] (1) Dissolve 1.309 g Ni(NO3)2·6H2O, 0.655 g Co(NO3)2·6H2O, and 0.677 g InN3O9·xH2O in 30 mL of deionized water, and denote this as solution A. Dissolve 1.276 g C2H2O4·2H2O in 30 mL of deionized water, and denote this as solution B. Titrate solution B slowly into solution A using a constant pressure burette (titate rate 1.5–3 mL / min), and stir magnetically for 60 min during and after titration. Transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene and maintain it at 120 °C for 12 h. After cooling to room temperature, a light blue precipitate is obtained. Centrifuge the obtained precipitate and wash it three times each with deionized water and ethanol.

[0038] (2) The light blue precipitate obtained by centrifugation was placed in a vacuum drying oven at 60°C and vacuum dried for 20-24 hours. The resulting light blue powder is the Ni-Co-In alloy precursor.

[0039] (3) Alloy particles were synthesized from Ni-Co-In alloy precursor powder prepared by heating in a CH4-Ar mixed flow (CH4 / Ar=1) at a total flow rate of 40 mL / min. The precursor was heated to 450 °C and maintained for 30 min to dehydrate and decompose the Ni-Co-In alloy precursor into Ni-Co-In alloy, which was named Ni 0.50 Co 0.25 In 0.25 .

[0040] Example 2

[0041] This embodiment synthesizes Ni 0.55 Co 0.20 In 0.25 The process of alloy catalysts is as follows:

[0042] (1) Dissolve 1.439 g Ni(NO3)2·6H2O, 0.524 g Co(NO3)2·6H2O, and 0.677 g InN3O9·xH2O in 30 mL of deionized water, and denote this as solution A. Dissolve 1.276 g C2H2O4·2H2O in 30 mL of deionized water, and denote this as solution B. Titrate solution B slowly into solution A using a constant pressure burette (tipping rate 1.5–3 mL / min), and stir magnetically for 60 min during and after the titration. Transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene and maintain it at 120 °C for 12 h. After cooling to room temperature, a light blue precipitate is obtained. Centrifuge the obtained precipitate and wash it three times each with deionized water and ethanol.

[0043] (2) The light blue precipitate obtained by centrifugation was placed in a vacuum drying oven at 60°C and vacuum dried for 24 hours. The resulting light blue powder is the Ni-Co-In alloy precursor.

[0044] (3) Alloy particles were synthesized from Ni-Co-In alloy precursor powder prepared by heating in a CH4-Ar mixed flow (CH4 / Ar=1) at a total flow rate of 40 mL / min. The precursor was heated to 450 °C and maintained for 30 min to dehydrate and decompose the Ni-Co-In alloy precursor into Ni-Co-In alloy, which was named Ni 0.55 Co 0.20 In 0.25 .

[0045] Example 3

[0046] This embodiment synthesizes Ni 0.60 Co 0.15 In 0.25 The process of alloy catalysts is as follows:

[0047] (1) Dissolve 1.570g Ni(NO3)2·6H2O, 0.393g Co(NO3)2·6H2O, and 0.677g InN3O9·xH2O in 30mL of deionized water, and denote this as solution A. Dissolve 1.276g C2H2O4·2H2O in 30mL of deionized water, and denote this as solution B. Titrate solution B slowly into solution A using a constant pressure burette (titate rate 1.5–3 mL / min), and stir magnetically for 60 min during and after titration. Transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene and maintain it at 120℃ for 12 h. After cooling to room temperature, a light blue precipitate is obtained. Centrifuge the obtained precipitate and wash it three times each with deionized water and ethanol.

[0048] (2) The light blue precipitate obtained by centrifugation was placed in a vacuum drying oven at 60°C and vacuum dried for 24 hours. The resulting light blue powder is the Ni-Co-In alloy precursor.

[0049] (3) Alloy particles were synthesized from Ni-Co-In alloy precursor powder prepared by heating in a CH4-Ar mixed flow (CH4 / Ar=1) at a total flow rate of 40 mL / min. The precursor was heated to 450 °C and maintained for 30 min to dehydrate and decompose the Ni-Co-In alloy precursor into Ni-Co-In alloy, which was named Ni 0.60 Co 0.15 In 0.25 .

[0050] Example 4

[0051] This embodiment synthesizes Ni 0.65 Co 0.10 In 0.25 The process of alloy catalysts is as follows:

[0052] (1) Dissolve 1.701g Ni(NO3)2·6H2O, 0.262g Co(NO3)2·6H2O, and 0.677g InN3O9·xH2O in 30mL of deionized water, and denote this as solution A. Dissolve 1.276g C2H2O4·2H2O in 30mL of deionized water, and denote this as solution B. Titrate solution B slowly into solution A using a constant pressure burette (tipping rate 1.5–3 mL / min), and stir magnetically for 60 min during and after the titration. Transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene and maintain it at 120℃ for 12 h. After cooling to room temperature, a light blue precipitate is obtained. Centrifuge the obtained precipitate and wash it three times each with deionized water and ethanol.

[0053] (2) The light blue precipitate obtained by centrifugation was placed in a vacuum drying oven at 60°C and vacuum dried for 24 hours. The resulting light blue powder is the Ni-Co-In alloy precursor.

[0054] (3) Alloy particles were synthesized from Ni-Co-In alloy precursor powder prepared by heating in a CH4-Ar mixed flow (CH4 / Ar=1) at a total flow rate of 40 mL / min. The precursor was heated to 450 °C and maintained for 30 min to dehydrate and decompose the Ni-Co-In alloy precursor into Ni-Co-In alloy, which was named Ni 0.65 Co 0.10 In 0.25 .

[0055] Example 5

[0056] This embodiment synthesizes Ni0.70 Co 0.05 In 0.25 The process of alloy catalysts is as follows:

[0057] (1) Dissolve 1.832g Ni(NO3)2·6H2O, 0.131g Co(NO3)2·6H2O, and 0.677g InN3O9·xH2O in 30mL of deionized water, and denote this as solution A. Dissolve 1.276g C2H2O4·2H2O in 30mL of deionized water, and denote this as solution B. Titrate solution B slowly into solution A using a constant pressure burette (titate rate 1.5–3 mL / min), and stir magnetically for 60 min during and after the titration. Transfer the suspension to a stainless steel autoclave lined with polytetrafluoroethylene and maintain it at 120℃ for 12 h. After cooling to room temperature, a light blue precipitate is obtained. Centrifuge the obtained precipitate and wash it three times each with deionized water and ethanol.

[0058] (2) The light blue precipitate obtained by centrifugation was placed in a vacuum drying oven at 60°C and vacuum dried for 24 hours. The resulting light blue powder is the Ni-Co-In alloy precursor.

[0059] (3) Alloy particles were synthesized from Ni-Co-In alloy precursor powder prepared by heating in a CH4-Ar mixed flow (CH4 / Ar=1) at a total flow rate of 40 mL / min. The precursor was heated to 450 °C and maintained for 30 min to dehydrate and decompose the Ni-Co-In alloy precursor into Ni-Co-In alloy, which was named Ni 0.70 Co 0.05 In 0.25 .

[0060] Example of effect

[0061] (1) X-ray powder diffraction was used to detect the Ni-Co-In ternary alloy powders prepared in Examples 1-5 with different proportions. The detection results are as follows: Figure 1 As shown, through Figure 1 It can be seen that the XRD patterns of all alloy samples show only a series of peaks corresponding to the face-centered cubic (fcc) phase, indicating the formation of a Ni-Co-In solid solution, unlike the individual diffraction peaks exhibited by physically mixed metal samples. Further calculations revealed that the grain size of the Ni-Co-In alloy particles ranged from 15.6 to 18.8 nm.

[0062] (2) Ni-Co-In ternary alloy powders prepared in different proportions in Examples 1 to 5 were used as catalysts to catalyze the methane cracking reaction.

[0063] Specifically, a fixed mass of Ni-Co-In alloy catalyst was placed in the center of the quartz tube reactor. To ensure that equal mass of sample was used in each test, it was assumed that the contact time of methane on the catalyst particles was approximately the same in each test. A type K thermocouple covered with a quartz thermocouple sheath was placed near the catalyst bed to monitor its temperature. The reactor was vertically mounted in an electric furnace, and the methane cracking experiment was conducted under standard atmospheric pressure. The feed gas was CH4, and the gas flow rate was 6 mL / min. The intelligent electric furnace heated the center of the reaction tube to a reaction temperature of 800℃ (under a protective atmosphere with an Ar flow rate of 100 mL / min). Once the reactor temperature reached the set temperature, the feed gas was introduced to begin the catalytic methane cracking reaction. After 30 minutes of reaction, the catalyst was examined using X-ray powder diffraction. The results are as follows: Figure 2 As shown in the figure, diffraction peaks of graphite carbon and Ni-Co-In alloy can be observed, indicating that the catalyst still exists in the alloy state after the methane cracking reaction.

[0064] (3) The Ni prepared in Example 4 were respectively tested. 0.65 Co 0.10 In 0.25 The alloy catalyst and its microstructure after undergoing the methane cracking reaction as described in (2) were characterized, and SEM images are shown below. Figure 3 and Figure 4 As shown, by Figure 3 It is known that most Ni-Co-In particles are blocky, with rough surfaces and varying particle sizes. The catalyst surface has a large number of porous structures, which helps to provide more reaction sites and increase the catalyst's activity. Figure 4 It can be seen that Ni 0.65 Co 0.10 In 0.25 The alloy catalyst generates a large number of tubular carbon nanofibers after the methane cracking reaction. These are carbon nanotubes or carbon nanofibers with diameters in the nanometer range and lengths in the micrometer range. The white particles in the image are Ni-Co-In alloy particles after the catalytic reaction; they are located at the tips of the tubular carbon nanomaterials, indicating that the growth of the carbon nanotubes follows a tip-growth mechanism. Analysis reveals that not all Ni-Co-In alloy particles are completely encapsulated by carbon material, which is one reason for the catalyst's high stability.

[0065] (4) The Ni prepared in Example 4 0.65 Co 0.10 In 0.25 The alloy catalyst was used to perform methane cracking reactions at different temperatures, and the carbon products were then characterized by Raman spectroscopy. Specifically, Ni... 0.65 Co 0.10 In 0.25The Raman spectra of the deposited carbon in the product after catalytic cracking of methane at reaction temperatures of 700℃, 800℃, 900℃, and 990℃ for 30 min are shown below. Figure 5 As shown, the I of deposited carbon D / I G The values ​​were 1.26, 0.77, 0.40, and 1.46, respectively. The carbon I of the product at 900℃... D / I G The value is relatively small (0.40), indicating a high degree of graphitization.

[0066] Further analysis of the Ni prepared in Example 4 0.65 Co 0.10 In 0.25 The methane conversion rate of the alloy catalyst during the methane cracking reaction at different temperatures was characterized. Specifically, the methane catalytic cracking reaction was carried out at a reaction temperature of 700–990 °C for 10 min, and the methane conversion rate was as follows: Figure 7 As shown, since the methane cracking reaction is an endothermic reaction, increasing the reaction temperature greatly increases the methane conversion rate. When the reaction temperature is increased from 700℃ to 990℃, the methane conversion rate increases from 40% to 91%.

[0067] (5) The catalytic activity of the five Ni-Co-In alloy catalysts prepared in Examples 1-5 with different proportions was tested for methane cracking in a fixed-bed reactor (timing started when the reactor temperature reached 800℃, and the reaction time was 30 min). Figure 6 It can be seen that the methane conversion rate of the prepared Ni-Co-In alloys with different proportions increases with the increase of nickel molar fraction (or the decrease of cobalt molar fraction). However, when the nickel content is too high, the number of metallic nickel particles on the catalyst surface increases, making the relative spacing between these particles smaller, which easily leads to sintering or the formation of larger particles, thus affecting the catalyst activity. Specifically, the Ni prepared in Example 4... 0.65 Co 0.10 In 0.25 The catalytic activity and stability of the sample were both superior to those of other samples.

[0068] (6) The catalytic stability of the five Ni-Co-In alloy catalysts with different proportions prepared in Examples 1-5 was characterized at 800℃. Figure 8 As shown, all catalyst samples exhibited high initial catalytic activity because they underwent a decomposition reaction to convert nickel cobalt indium oxalate into a Ni-Co-In alloy before the reaction began. Within 120 min of the methane catalytic cracking reaction, the methane conversion rate of the catalyst samples showed almost no decreasing trend, with Ni... 0.50 Co 0.25 In 0.25The conversion rate of the alloy sample decreased slightly after 90 minutes of reaction. This indicates that the Ni-Co-In alloy catalyst prepared in this invention has good stability.

[0069] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing an alloy catalyst for catalyzing methane cracking reactions, characterized in that, include: (1) Oxalic acid solution was added dropwise to a mixed solution containing nickel nitrate, cobalt nitrate and indium nitrate. After the addition was completed, the solution was transferred to a high-pressure reactor for hydrothermal reaction. After the reaction was completed, the precipitate was washed and dried to obtain the Ni-Co-In alloy precursor. (2) Under a CH4-Ar mixed flow atmosphere, the Ni-Co-In alloy precursor was heat-treated to obtain the Ni-Co-In alloy catalyst; The heat treatment temperature in (2) is 200~600℃ and the time is 30~90min.

2. The preparation method according to claim 1, characterized in that, (1) The hydrothermal reaction temperature is 100~200℃ and the time is 10~20h.

3. The preparation method according to claim 1, characterized in that, (1) The drying conditions are: vacuum drying at 40~80℃ for 24~48h.

4. The preparation method according to claim 1, characterized in that, (2) The flow rate of the CH4-Ar mixture is 20~80 mL / min.

5. The preparation method according to claim 1 or 4, characterized in that, (2) The volume ratio of CH4 to Ar in the CH4-Ar mixed flow is 1:

1.

6. An alloy catalyst obtained by the preparation method according to any one of claims 1 to 5.

7. The application of the alloy catalyst according to claim 6, characterized in that, Used to catalyze methane cracking reactions.

8. A method for low-temperature catalytic cracking of methane, characterized in that, Using the alloy catalyst described in claim 6 as the catalyst for the pyrolysis reaction, the pyrolysis reaction conditions are as follows: under standard atmospheric pressure, the reaction temperature is 700~990℃, the CH4 gas flow rate is 6~60mL / min, and the protective gas Ar flow rate is 10~100mL / min.

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