Iron-rich hydrotalcite-like derivative catalyst for methane pyrolysis and preparation method thereof
Iron-rich hydrotalcite-like derivative catalysts were prepared by co-precipitation, which solved the problems of high energy consumption and poor dispersibility of traditional iron-based catalysts in methane catalytic cracking. This resulted in a highly efficient and stable methane pyrolysis reaction, reducing production costs and carbon dioxide emissions.
Patent Information
- Application Number
- CN202410559086.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-08
- Publication Date
- 2025-11-11
AI Technical Summary
Existing methane catalytic cracking hydrogen production technologies suffer from high energy consumption, high production costs, and high carbon dioxide emissions. Furthermore, traditional iron-based catalyst synthesis methods struggle to achieve uniform dispersion and high catalytic activity.
Iron-rich hydrotalcite-like derivative catalysts were synthesized by co-precipitation method. Using Fe2+ and Fe3+ as iron sources and M3+ or M4+ as support sources, a catalyst with uniform dispersion was prepared, which increased the iron content and ensured that the molar content of trivalent and above metal ions was between 0.2 and 0.33. After calcination, a catalyst with high specific surface area and small crystallite size was obtained.
It achieves high catalytic activity and good stability in the methane pyrolysis reaction, reduces the amount of catalyst support used, simplifies product separation, and improves the pyrolysis efficiency and lifespan of the catalyst.
Smart Images
Figure CN120920001A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of industrial catalysis, specifically to an iron-rich hydrotalcite-like derivative catalyst for the catalytic pyrolysis of methane and its preparation method. Technical Background
[0002] Hydrogen possesses advantages such as high energy density, high calorific value, abundant reserves, storability, renewability, power generation, zero pollution, and zero carbon emissions. Therefore, hydrogen energy is hailed as the "ultimate energy" of the 21st century and holds promise for solving current energy crises and environmental pollution. Since hydrogen is a secondary energy source, it must be produced from hydrogen-containing compounds. Methane, being the hydrocarbon with the highest hydrogen content and widely available (e.g., natural gas and biogas from anaerobic digestion of wet waste), is currently the primary raw material for industrial hydrogen production. Common hydrogen production methods include methane steam reforming, partial methane oxidation, methane catalytic cracking, coal gasification, methanol decomposition, ammonia decomposition, water electrolysis, photocatalytic water splitting, and biomass conversion (X. Qian X, Chen T, Enakonda L, et al. Methane decomposition to produce CO). x -freehydrogen and nano-carbon over metal catalysts: a review [J]. International Journal of Hydrogen Energy, 2020, 45: 7981-8001.). Among them, methane steam reforming for hydrogen production has the largest scale, accounting for about 50% of the world's hydrogen production. However, this method has high energy consumption, high production cost, and high carbon dioxide emissions. Methane catalytic cracking for hydrogen production technology is relatively mature, has a relatively small investment scale, and does not emit pollutants such as carbon dioxide during the production process. It can simultaneously produce high-quality green hydrogen and high-value-added functional carbon nanomaterials (Mondal K, Chandran S. Evaluation of the economic impact of hydrogen production by methane decomposition with steam reforming of methane process [J]. International Journal of Hydrogen Energy, 2014, 39: 9670-4.). Therefore, methane catalytic cracking for hydrogen production has received widespread attention in recent years and is expected to become an efficient and environmentally friendly hydrogen production technology to replace traditional hydrogen production processes such as methane steam reforming.
[0003] Using a suitable catalyst can reduce the methane cracking reaction temperature and shorten the reaction time. Currently, relevant research at home and abroad mainly focuses on low-cost nickel (Ni)-based and iron (Fe)-based catalysts and their binary or multi-alloy catalysts. Compared with nickel, iron is more environmentally friendly and cheaper (the price is only 1 / 200 of nickel). In addition, iron has a higher melting point than nickel. Research shows that iron-based catalysts can carry out catalytic reactions between 700 - 950 °C, while the applicable temperature of nickel-based catalysts is 500 - 700 °C. Since the methane catalytic pyrolysis reaction is an endothermic reaction, iron-based catalysts will have a better thermodynamic conversion rate than nickel-based catalysts. Currently, common synthesis methods of iron-based catalysts include impregnation method, fusion method, and sol-gel method. (Zhoua L, Enakondaa L, Harb M, et al. Fe catalysts for methane decomposition to produce hydrogen and carbon nano materials[J]. Applied Catalysis B: Environmental, 2017, 208: 44 - 59.). Summary of the Invention
[0004] Based on the above research background, the present invention provides an iron-rich hydrotalcite derivative catalyst for methane pyrolysis and its preparation method, aiming to use this catalyst for methane pyrolysis catalytic reaction to obtain hydrogen and economically valuable nano-carbon products. The following are the technical solutions of the present invention:
[0005] The first aspect of the present invention provides an iron-rich hydrotalcite derivative catalyst for methane pyrolysis. This derivative catalyst is obtained by calcining an iron-containing hydrotalcite precursor, and the structural formula of the hydrotalcite precursor is [Fe 2+ 1-x (Fe 3+ y M 3+ z )(OH)2][A n- x / n ·H2O or [Fe 2+ 1-i (Fe 3+ j M 4+ k )(OH)2][A n- (j+2k) / n ·mH2O; wherein, in the structural formula of the hydrotalcite precursor, y + z = x and 0.2 < x < 0.33, or j + k = i and 0.2 < i < 0.33, A n- It is an inorganic or organic anion, n is the charge number of the anion, and M is a metallic element. 3+ and M 4+ It is a metal cation, m>0.
[0006] For example, the anion can be Cl. - F - CO3 2- NO3 - Fe(CN)6 4- Fe(CN)6 3- Mo7O 24 6- W7O 24 6- V 10 O 28 6- OsO4 2- PMo 12 O 40 3- PW 12 O 40 3- Or PW6Mo6O 40 3- .
[0007] For example, the metal cation can be Al. 3+ Co 3+ Mn 3+ Ga 3+ Cr 3+ or Zr 4+ .
[0008] In the structural formula of the hydrotalcite-like precursor, H2O represents bound water, and m is the stoichiometric amount of H2O.
[0009] The second aspect of the present invention provides a method for preparing the above-mentioned derivative catalyst, comprising the following steps: synthesizing an iron-containing hydrotalcite-like precursor by co-precipitation, drying, and calcining to form the derivative catalyst.
[0010] The specific steps of the coprecipitation method are as follows: Prepare a soluble metal salt solution of Fe and M, an alkaline anion solution, and an alkaline solution according to the structural formula and proportions of the hydrotalcite-like precursor. Add the soluble metal salt solution dropwise to the alkaline anion solution, while simultaneously adding the alkaline solution dropwise to maintain the pH of the solution at 10 ± 0.5. Under room temperature conditions and a non-oxidizing gas protection environment, a coprecipitation reaction occurs to generate a precipitate, which is the hydrotalcite-like precursor. The precipitate is the hydrotalcite-like precursor.
[0011] For example, the non-oxidizing gas can be nitrogen, helium, etc.
[0012] For example, the anion in the alkaline anion solution can be Cl-. - F - CO3 2- NO3 - Fe(CN)6 4- Fe(CN)6 3- Mo7O 24 6- W7O 24 6- V 10 O 28 6- OsO4 2- PMo 12 O 40 3- PW 12 O 40 3- or PW6Mo6O 40 3- .
[0013] For example, the alkaline solution may be a potassium hydroxide solution, sodium hydroxide solution, barium hydroxide solution, ammonia water, or lithium hydroxide solution.
[0014] Furthermore, during the coprecipitation reaction, the soluble metal salt solution and the alkaline solution are stirred to promote the reaction. After the reaction is completed, stirring is stopped, and the mixture is aged and left to stand at room temperature, preferably for 12 hours.
[0015] Furthermore, in the coprecipitation method, a reduced pressure filtration method is used to obtain a precipitate from which the liquid has been removed.
[0016] As an example, the drying is vacuum drying, preferably vacuum drying at 80°C for 24 hours.
[0017] Furthermore, the calcination temperature is 400–800°C, and the calcination time is 2–5 hours, preferably 3 hours at 450°C.
[0018] Compared with existing inventions, the present invention has the following advantages:
[0019] (1) The present invention uses a co-precipitation method to synthesize a hydrotalcite-like precursor, which can uniformly disperse iron (Fe) ions and support (M) ions.
[0020] (2) Simultaneous use of Fe 2+ and Fe 3+ As a source of iron metal, M is used 3+ Or M 4+This serves as a catalyst support source. This not only increases the iron content in the catalyst but also ensures that the molar content (x or i) of trivalent or higher metal ions is between 0.2 and 0.33, thereby obtaining a hydrotalcite-like precursor.
[0021] (3) The hydrotalcite-like precursor has a large specific surface area, thus a uniformly dispersed catalyst with a large specific surface area can be obtained after calcination. Furthermore, the catalyst also has a small crystallite size. Both of these factors are beneficial for the catalytic pyrolysis of methane. The catalyst described in this invention exhibits highly efficient methane pyrolysis catalytic activity and good stability.
[0022] (4) Compared with the traditional impregnation method, the method of the present invention requires less oxide of M as catalyst support, which is beneficial to remove it from the product after the catalytic pyrolysis reaction of methane. Attached Figure Description
[0023] Figure 1 A schematic diagram of the synthesis of a hydrotalcite-like derivative catalyst according to the present invention.
[0024] Figure 2 XRD pattern of hydrotalcite precursor in Example 1 ( Figure 2 a) Catalyst spectrum of hydrotalcite derivatives ( Figure 2 b)
[0025] Figure 3 Methane conversion over time in Example 2
[0026] Figure 4 Gas chromatogram of the methane cracking reaction in Example 2 after 5 hours.
[0027] Figure 5 Physical image of carbon products from the catalytic pyrolysis of methane in Example 2
[0028] Figure 6 Transmission electron microscopy (TEM) image of the carbon product in Example 2
[0029] Figure 7 XRD pattern of hydrotalcite precursor in Example 3 ( Figure 7 a) Catalyst spectrum of hydrotalcite derivatives ( Figure 7 b)
[0030] Figure 8 Methane conversion over time in Example 4 Detailed Implementation
[0031] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.
[0032] In this invention, room temperature refers to 1-30°C.
[0033] See Figure 1 This invention first synthesizes a hydrotalcite-like precursor via co-precipitation. After processing the precursor, an iron-rich hydrotalcite-like derivative catalyst for methane pyrolysis is obtained. The experimental equipment required for the co-precipitation method includes a pH meter 1, a nitrogen (N2) delivery tube 2, a peristaltic pump delivery tube for a metal solution 3, a peristaltic pump delivery tube for a sodium hydroxide (NaOH) solution 4, a three-necked round-bottom flask 5, a sodium carbonate (Na2CO3) solution 6, and a magnetic stir bar 7. The pH meter 1 is used to monitor the pH of the solution. The N2 delivery tube 2 is used to bubble N2 into the three-necked round-bottom flask 5 to isolate it from air. The peristaltic pump delivery tube 3 is used to dropwise add a metal mixture solution containing ferrous ions (Fe2+) into the three-necked round-bottom flask 5 at a constant flow rate. 2+ ) and iron ions (Fe 3+ ) and other metal ions used as catalyst supports (M 3+ Or M 4+ The NaOH solution peristaltic pump conduit 4 is used to add NaOH solution dropwise to the three-necked round-bottom flask 5 at a constant flow rate to maintain the pH of the system at 10 ± 0.5. The Na₂CO₃ solution 6 is used to provide CO₃²⁻ to the reaction process. 2- Source. The magnetic stir bar 7 is used to stir the reaction solution.
[0034] After the co-precipitation reaction is completed and the mixture is aged for a certain period of time, a hydrotalcite-like precursor 9 can be obtained by centrifugation or vacuum filtration 8. The hydrotalcite-like precursor 9 is dried and then calcined 11 to obtain an iron-rich hydrotalcite-like derivative catalyst 12.
[0035] Iron-rich hydrotalcite-like derivative catalyst 12 can be directly used in the catalytic pyrolysis of methane.
[0036] The present invention will be further described below with reference to embodiments:
[0037] Example 1
[0038] In this embodiment, referring to the synthesis steps of the above-described iron-rich hydrotalcite-like derivative catalyst, Fe... 2+ ,Fe 3 + And Al 3+As a precursor and catalyst for the synthesis of hydrotalcite-like substances and hydrotalcite-like derivatives from mixed metal ion solutions.
[0039] First, prepare 1M Na₂CO₃ in a three-necked round-bottom flask. Then, prepare a 1M Fe₂CO₃ solution using FeCl₂·4H₂O, Fe(NO₃)₃·9H₂O, and Al(NO₃)₃·9H₂O. 2+ ,Fe 3+ And Al 3+ A mixed metal ion solution, wherein the metal ions are in the following ratio: Fe 2+ :Fe 3+ :Al 3+ = 7:1:2. Then prepare a 2M NaOH solution. At room temperature (25°C), first, continuously stir the Na2CO3 solution in the three-necked round-bottom flask and purge with N2 at a rate of 50 standard mL / min for at least 20 minutes to remove air from the solution and the flask. Simultaneously, a 1M metal ion mixed solution is also bubbled in with N2 at a rate of 45 sccm to prevent Fe... 2+ Oxidized by air to Fe 3+ After removing air, a peristaltic pump was started, and a mixed solution of metal ions was added dropwise to a three-necked round-bottom flask at a rate of 1.5 mL / min through the peristaltic pump tubing. During this process, the pH of the reaction solution in the three-necked round-bottom flask was monitored using a pH meter. When the pH of the reaction solution fell below 10, another peristaltic pump was started, and NaOH solution was added dropwise to the three-necked round-bottom flask at a rate of 1.5 mL / min through the peristaltic pump tubing to maintain the pH of the reaction solution between 9.5 and 10.5. After the addition of the mixed solution of metal ions was completed, stirring was continued for 1 hour (h), followed by aging for 12 hours. The precipitate was then filtered under reduced pressure to obtain a blue-green hydrotalcite-like precursor, which was then dried in a vacuum drying oven at 80°C for 24 hours. The dried hydrotalcite-like precursor was then calcined in a muffle furnace at 450°C for 3 hours to obtain a hydrotalcite-like derivative catalyst.
[0040] In this embodiment, the structures of the synthesized hydrotalcite precursor and its derivative catalyst were verified by X-ray powder diffraction (XRD) testing (e.g., Figure 2 As shown). Figure 2 As shown in a, the dried hydrotalcite-like precursor (Fe) 2+ 0.7 Fe 3 + 0.1 Al 0.2 -P) at a 2θ angle of 11.8°, a hydrotalcite-like Fe4Al2(OH) 12 The characteristic diffraction peaks of CO3·3H2O (PDF#51-1527, caresite-3T) are weak. This may be due to the weak characteristic diffraction peaks of Fe.2+ and Fe 3+ Simultaneously, hydrotalcite-like precursors also contain hydrotalcite-like [Fe] 2+ 1-x Fe 3+ x [(OH)2](CO3) x / 2 ·mH₂O. This structure is easily oxidized to Fe₃O₄ during vacuum drying. Therefore, from Figure 2 As can be seen in a, the hydrotalcite-like precursor (Fe) 2+ 0.7 Fe 3+ 0.1 Al 0.2 Characteristic diffraction peaks of Fe3O4 appeared at 35.5, 40.1, and 62.7 degrees Celsius. After calcining the dried precursor at 450℃ for 3 h, a hydrotalcite-like derivative catalyst (Fe3O4) was obtained. 2+ 0.7 Fe 3+ 0.1 Al 0.2 -O). From Figure 2 The characteristic diffraction peaks of Al2O3 are not visible in b, but Fe... 2+ 0.7 Fe 3+ 0.1 Al 0.2 -O showed diffraction peaks for Fe2O3 (PDF#01-1053, hematite) at 33.2, 35.7, and 64.1, indicating that Fe... 2+ Fe 3+ Al 0.2 -O contains Fe2O3. Fe can also be seen. 2+ Fe 3+ Al 0.2 The characteristic diffraction peaks of -O have relatively large peak widths, indicating that the co-precipitation method can make Al... 3+ Uniformly dispersed in Fe 2+ and Fe 3+ This process prevents the formation of large Fe2O3 crystals after calcination. Fe can be calculated using the Scherrer equation. 2+ Fe 3+ Al 0.2 The grain size of Fe2O3 in -O is approximately 18.4 nanometers.
[0041] When x or i is between 0.2 and 0.33, in addition to trivalent Al ions, other trivalent or tetravalent M ions will also be uniformly dispersed among the iron ions, just like Al ions. This prevents the formation of large Fe2O3 crystals after calcination and instead forms Fe2O3 crystals with smaller crystal sizes.
[0042] Example 2
[0043] In this embodiment, in order to verify the hydrotalcite-like derivative catalyst (Fe) 2+ 0.7 Fe 3+ 0.1 Al 0.2 The catalytic pyrolysis performance of methane (-O) was evaluated using a fixed-bed reactor. The specific steps included:
[0044] (1) Weigh 0.1g Fe 2+ 0.7 Fe 3+ 0.1 Al 0.2 -O catalyst was placed in an alumina boat, and then the alumina boat was placed in a quartz tube of a fixed-bed reactor.
[0045] (2) Introduce N2 at a flow rate of 45 sccm into the fixed bed reactor and raise the temperature of the quartz tube from 20 degrees to 710 degrees at a heating rate of 10℃ / min.
[0046] (3) After the temperature reaches 710℃, stop the N2 flow and then introduce methane gas at a flow rate of 4 sccm.
[0047] (4) Connect a gas chromatograph to the back end of the reactor and detect the gaseous products every 15 minutes.
[0048] (5) Stop the reaction after 10 hours, take out the alumina boat and weigh the nano carbon product inside.
[0049] In this embodiment, the pyrolysis reaction process of methane is shown in the following reaction formula:
[0050] CH4→2H2+C
[0051] In this embodiment, the conversion rate of methane was calculated by measuring the methane content using gas chromatography. Figure 3 Demonstrated in the catalyst Fe 2+ 0.7 Fe 3+ 0.1 Al 0.2 The conversion efficiency of methane over time is affected by -O. At 0.75 h, the methane conversion rate reaches as high as 88.0%, which should be attributed to Fe. 2+ 0.7 Fe 3+ 0.1 Al 0.2The Fe₂O₃ in the -O phase reacts with methane to be reduced to Fe, which is then further reduced to Fe₃C, consuming methane. Subsequently, Fe₃C acts as the true catalytic active center, catalyzing the cracking of methane. The methane conversion reaches a peak of 65.6% at 1.5 h, then gradually decreases, maintaining a conversion of 53.4% after 10 h, indicating that the catalyst synthesized in this patent has good stability and lifespan.
[0052] Figure 4 The gas chromatogram of the methane cracking reaction after 5 hours is given.
[0053] After the reaction was complete and the temperature of the fixed-bed reactor cooled to room temperature, the carbon product was removed and weighed; its weight was 0.9243 g. A picture of the carbon product is shown below. Figure 5 As shown. The transmission electron microscope image of the obtained carbon product is shown below. Figure 6 As shown, the obtained carbon product is proven to be carbon nanotubes (CNTs).
[0054] Example 3
[0055] In this embodiment, to demonstrate the importance of the catalyst support (oxide of metal M), the synthesis steps for the iron-rich hydrotalcite-like derivative catalyst described above are followed, using only Fe... 2+ and Fe 3+ As a precursor and catalyst for the synthesis of hydrotalcite-like substances and hydrotalcite-like derivatives from mixed metal ion solutions.
[0056] First, prepare 1M Na₂CO₃ in a three-necked round-bottom flask. Then, prepare a 1M Fe solution using FeCl₂·4H₂O and Fe(NO₃)₃·9H₂O. 2+ , and Fe 3+ A mixed metal ion solution, wherein the metal ions are in the following ratio: Fe 2+ :Fe 3+ =7:3. Then prepare a 2M NaOH solution. At room temperature (25°C), first, continuously stir the Na2CO3 solution in the three-necked round-bottom flask and bubble in N2 at 50 standard mL / min for at least 20 minutes to remove air from the solution and the three-necked round-bottom flask. Simultaneously, a 1M metal ion mixed solution is also bubbled in with N2 at 45 sccm to prevent Fe... 2+ Oxidized by air to Fe 3+After removing air, a peristaltic pump was started, and a mixed solution of metal ions was added dropwise to a three-necked round-bottom flask at a rate of 1.5 mL / min through the peristaltic pump tubing. During this process, the pH of the reaction solution in the three-necked round-bottom flask was monitored using a pH meter. When the pH of the reaction solution fell below 10, another peristaltic pump was started, and NaOH solution was added dropwise to the three-necked round-bottom flask at a rate of 1.5 mL / min through the peristaltic pump tubing to maintain the pH of the reaction solution between 9.5 and 10.5. After the addition of the mixed solution of metal ions was completed, stirring was continued for 1 hour, followed by aging for 12 hours. The precipitate was then filtered under reduced pressure to obtain a blue-green hydrotalcite-like precursor, which was then dried in a vacuum drying oven at 80°C for 24 hours. The dried hydrotalcite-like precursor was then calcined in a muffle furnace at 450°C for 3 hours to obtain a hydrotalcite-like derivative catalyst (Fe₂O₃).
[0057] In this embodiment, the structures of the synthesized hydrotalcite precursor and its derivative catalyst were verified by X-ray powder diffraction (XRD) testing (e.g., Figure 7 As shown). Figure 7 As shown in a, the dried hydrotalcite-like precursor (Fe) 2+ 0.7 Fe 3 + 0.3 -P) No hydrotalcite-like material [Fe] was observed at a 2θ angle of 11.1°. 2+ 1-x Fe 3+ x [(OH)2](CO3) x / 2 The characteristic diffraction peaks of ·mH2O are due to the fact that this structure is easily oxidized to Fe3O4 during vacuum drying. Therefore, from Figure 7 As can be seen in a, the hydrotalcite-like precursor (Fe) 2+ 0.7 Fe 3+ 0.3 The presence of characteristic diffraction peaks for Fe3O4 at 35.5, 40.1, and 62.7 °C indicates the formation of Fe3O4 after drying. The dried precursor was calcined at 450 °C for 3 h to obtain a hydrotalcite-like derivative catalyst (Fe...). 2 + 0.7 Fe 3+ 0.3 -O). From Figure 7 Fe can be seen in b. 2+ 0.7 Fe 3+ 0.3The presence of Fe₂O₃ (PDF#01-1053, hematite) diffraction peaks at 33.2, 35.7, and 64.1 nm indicates that the hydrotalcite-like precursor was transformed into Fe₂O₃ after calcination. Calculations using the Scherrer equation show that the grain size of Fe₂O₃ is approximately 39.3 nm, which is larger than that of Fe. 2+ 0.7 Fe 3+ 0.1 Al 0.2 The Fe2O3 grain size in -O is larger (18.4 nm). This indicates the absence of a carrier metal ion (M). 3+ Or M 4+ Dispersed in Fe 2+ and Fe 3+ During the calcination process, Fe ions are more likely to aggregate and form Fe2O3 with larger grain size.
[0058] Example 4
[0059] In this embodiment, in order to verify the hydrotalcite-like derivative catalyst (Fe) 2+ 0.7 Fe 3+ 0.3 The catalytic pyrolysis performance of the catalyst (O-) in methane was investigated, and the important role of the catalyst support (oxide of metal M) in the methane cracking reaction was verified. A fixed-bed reactor was used to evaluate the catalyst activity. The specific steps included:
[0060] (1) Weigh 0.1g Fe 2+ 0.7 Fe 3+ 0.3 -O catalyst was placed in an alumina boat, and then the alumina boat was placed in a quartz tube of a fixed-bed reactor.
[0061] (2) Introduce N2 at a flow rate of 45 sccm into the fixed bed reactor and raise the temperature of the quartz tube from 20 degrees to 710 degrees at a heating rate of 10℃ / min.
[0062] (3) After the temperature reaches 710℃, stop the N2 flow and then introduce methane gas at a flow rate of 4 sccm.
[0063] (4) Connect a gas chromatograph to the back end of the reactor and detect the gaseous products every 15 minutes.
[0064] (5) Stop the reaction after 10 hours, take out the alumina boat and weigh the nano carbon product inside.
[0065] In this embodiment, the pyrolysis reaction process of methane is shown in the following reaction formula:
[0066] CH4→2H2+C
[0067] In this embodiment, the conversion rate of methane was calculated by measuring the methane content using gas chromatography. Figure 8 Demonstrated in the catalyst Fe 2+ 0.7 Fe 3+ 0.3 The conversion efficiency of methane over time is affected by -O. At 0.75 h, the methane conversion rate reaches as high as 80.3%, which should be attributed to Fe. 2+ 0.7 Fe 3+ 0.1 Al 0.2 The Fe₂O₃ in the -O phase reacts with methane, being reduced to Fe, and then further reduced to Fe₃C, consuming methane. Subsequently, Fe₃C acts as the true catalytic active center, catalyzing the cracking of methane. However, after 1 hour of reaction, the methane conversion rate decreased to 50.5%, and after 2 hours, it decreased to 4.6%. This indicates that the lack of a catalyst support (the oxide of metal M) leads to catalyst aggregation and rapid deactivation during the catalytic process.
Claims
1. An iron-rich hydrotalcite-like derivative catalyst for methane pyrolysis, characterized in that, Obtained by calcining an iron-containing hydrotalcite-like precursor, the structural formula of the hydrotalcite-like precursor is [Fe 2+ 1-x (Fe 3+ y M 3+ z )(OH)2][A n- x / n ·H2O or [Fe 2+ 1-i (Fe 3+ j M 4+ k )(OH)2][A n- (j+2k) / n ·mH2O; wherein, in the structural formula of the hydrotalcite-like precursor, y + z = x and 0.2 < x < 0.33, or j + k = i and 0.2 < i < 0.33, A n- is an inorganic or organic anion, n is the charge carried by the anion, M is a metal element, M 3+ and M 4+ are metal cations, m > 0. 2. The catalyst according to claim 1, characterized in that, The anion is Cl. - F - CO3 2- NO3 - Fe(CN)6 4- Fe(CN)6 3- Mo7O 24 6- W7O 24 6- V 10 O 28 6- OsO4 2- PMo 12 O 40 3- PW 12 O 40 3- Or PW6Mo6O 40 3- .
3. The catalyst according to claim 1 or 2, characterized in that, The metal cation is Al. 3+ Co 3+ Mn 3+ Ga 3+ Cr 3+ or Zr 4+ .
4. The method for preparing the derivative catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: An iron-containing hydrotalcite-like precursor was synthesized by co-precipitation, and then dried and calcined to form the derivative catalyst.
5. The preparation method according to claim 4, characterized in that, The specific steps of the coprecipitation method are as follows: according to the structural formula ratio of the hydrotalcite-like precursor, prepare a soluble metal salt solution of Fe and M, an alkaline anion solution, and an alkaline solution. Add the soluble metal salt solution dropwise to the alkaline anion solution, and simultaneously add the alkaline solution dropwise to the alkaline anion solution to maintain pH = 10 ± 0.
5. Under room temperature conditions and non-oxidizing gas protection, a coprecipitation reaction occurs to generate a precipitate, which is the hydrotalcite-like precursor.
6. The preparation method according to claim 4 or 5, characterized in that, The calcination temperature is 400–800℃, and the calcination time is 2–5 hours.
7. The preparation method according to claim 5, characterized in that, The anion in the alkaline anion solution is Cl. - F - CO3 2- NO3 - Fe(CN)6 4- Fe(CN)6 3- Mo7O 24 6- W7O 24 6- V 10 O 28 6- OsO4 2- PMo 12 O 40 3- PW 12 O 40 3- Or PW6Mo6O 40 3- .
8. The preparation method according to claim 5, characterized in that, The alkaline solution is a potassium hydroxide solution, sodium hydroxide solution, barium hydroxide solution, ammonia water, or lithium hydroxide solution.
9. The preparation method according to claim 5, characterized in that, During the coprecipitation reaction, the soluble metal salt solution and the alkaline anion solution are stirred to promote the reaction. After the reaction is completed, stirring is stopped, and the mixture is aged and allowed to stand at room temperature. In the coprecipitation method, a precipitate is obtained by vacuum filtration to remove the liquid. The drying is vacuum drying. The non-oxidizing gas is nitrogen or helium.