A supported Ni-based catalyst and its preparation and application

Abstract

The present invention discloses a supported Ni-based catalyst and its preparation and application. The supported Ni-based catalyst is prepared by wet impregnation of Fe2O3-Al2O3 composite oxide as a carrier, loading nickel-containing inorganic salt, drying, calcination, hydrogen reduction, and passivation. The Fe2O3-Al2O3 composite oxide has a slit-type mesoporous structure. The supported Ni-based catalyst contains FeNi3 crystal phase and Ni 0 Crystalline phase; the Ni loading in the supported Ni-based catalyst is 20-30%. The present invention provides the use of the supported Ni-based catalyst in a low-temperature CO2 methanation reaction. The catalyst has the advantages of low raw material cost, simple preparation process, ease of industrial production, high loading, small metallic Ni particle size, and high low-temperature CO2 conversion and CH4 selectivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and specifically relates to a supported Ni-based catalyst and a preparation method thereof and a method for preparing the supported Ni-based catalyst at low temperature (<300 o C) Application in CO2 methanation reaction. Background Art

[0002] To address global warming caused by CO2 emissions, carbon capture, utilization, and storage (CCUS) technologies have attracted widespread attention for CO2 emission reduction and utilization [EC Ra et al, ACS Catal. 2020, 10, 11318-11345]. Among the various CCUS technologies, catalytic hydrogenation of CO2 to produce hydrocarbon fuels and other chemicals is currently the most attractive approach in the field of CO2 conversion. Among the products of CO2 hydrogenation, methane (CH4) is the primary component of natural gas. Compared with other fossil fuels, CH4 has a higher combustion value, is clean and safe, and can be transported through existing pipeline infrastructure. Therefore, using CO2 and green hydrogen as feedstocks, CO2 methanation to produce clean methane (a clean energy source currently attracting global attention) is one of the effective approaches to CO2 resource utilization (K. Stangeland, et al, Energy Procedia, 2017, 105, 2022-2027). It can not only promote CO2 emission reduction, but also alleviate the current shortage of natural gas resources in my country and reduce dependence on foreign natural gas resources.

[0003] The research and development of catalysts and catalytic reaction technologies are the core links in achieving efficient CO2 to methane production. Compared with precious metal catalysts such as Ru, Rh and Pd, Ni-based catalysts have the advantages of low price and excellent catalytic performance, making them the most promising CO2 methanation catalysts. Since CO2 methanation is a highly exothermic process ( , ΔH = -165.0 KJ / mol), so low reaction temperature is more conducive to CO2 conversion, and it can also effectively reduce the production of by-product CO and inhibit the sintering of catalyst particles. In addition, from the perspective of economic benefits, low-temperature CO2 methanation has lower energy consumption and is more economically valuable. However, the thermal stability of CO2 molecules is very high, which means that under low temperature conditions (for example: <300 oC) The CO2-to-methane conversion process is significantly kinetically limited. Consequently, due to the common thermodynamic-kinetic mismatch in CO2 methanation (low temperatures are thermodynamically favorable, but the reaction is kinetically limited at low temperatures), existing Ni-based catalysts suitable for CO2 methanation generally suffer from poor low-temperature catalytic performance, severely hindering the development and commercial application of low-temperature CO2 methanation processes [CQ Song, et al., Nature chemical engineering, 2024, 1, 638-649; J. Ashok, et al, Catalysis Today, 2020, 356, 471-489].

[0004] Support materials play a crucial role in influencing and regulating the performance of heterogeneous catalysts, typically affecting the dispersion of metal active sites, metal-support interactions, electron transfer between the metal and support, and oxygen vacancies on the catalyst surface. For low-temperature CO2 methanation, many traditional oxide supports (such as Al2O3 and SiO2) exhibit poor CO2 adsorption, resulting in poor catalytic performance. However, some metal oxides (such as ZrO2 and CeO2) possess redox properties and abundant oxygen vacancies, effectively promoting the activation of C=O bonds in CO2. When loaded with active metal Ni, the presence of hydroxyl groups and oxygen vacancies on the support surface actively promotes CO2 adsorption and conversion. Fu et al. introduced Al into Ni / CeO2 via a coprecipitation method to form a CeO2-Al2O3-supported Ni-based catalyst. They found that the addition of Al significantly enhanced the catalytic performance for low-temperature CO2 methanation. When the Al / Ce molar ratio was 0.1, the catalyst exhibited optimal performance at 240°C (CO2 conversion of 88.83% and CH4 selectivity of 99.96%). The addition of an appropriate amount of Al not only increased the specific surface area of ​​the catalyst but also maintained a moderately strong interaction between the metal Ni and the support, thereby promoting the formation of active metal Ni species. Furthermore, the presence of Al increased the oxygen vacancy concentration, promoting the generation of a large number of hydroxyl groups (-OH), thereby changing the distribution of basic sites on the catalyst surface and transforming the reaction pathway from a single CO pathway to a dual pathway of CO and formate coexisting [Fu et al., Chemical Engineering Journal, 2024, 489, 151021]. Fu et al. also introduced Al into the Ni / ZrO2 system to construct a Ni-based catalyst supported on a ZrO2-Al2O3 composite support. The addition of appropriate amount of Al significantly improved the dispersion of metal Ni on the catalyst surface, promoted the activation and dissociation of H2, and thus greatly improved the low temperature (<300℃) CO2 methanation activity (at 280°C, 48,000 h -1Under the conditions of 0.1 MPa and 0.2 MPa, the CO2 conversion rate of the catalyst Ni / Zr-Al-0.1 was 84.8%, and the CH4 selectivity was 99.4%). The study found that the Ni-based catalysts based on the ZrO2-Al2O3 composite support all followed the formate reaction path. Because the introduction of Al inhibited the activation ability of ZrO2 for H2, the active sites of the catalyst were transferred from the support surface to the support-Ni interface, thereby improving the hydrogenation reaction efficiency of the active intermediates [Fu H, et al., Journal of CO2Utilization, 2023, 69, 102415]. However, in the above scheme, the Ni-based catalyst used ZrO2 and CeO2, both of which are expensive, which is not conducive to the large-scale production of the catalyst and the commercial application and promotion of the low-temperature CO2 methanation process.

[0005] To address the above problems, the present invention uses a low-cost, high specific surface area, large pore size, mesoporous Fe2O3-Al2O3 composite oxide as a carrier to prepare a supported Ni-based catalyst to improve the low-temperature CO2 methanation reaction performance of the Ni-based catalyst. Summary of the Invention

[0006] In order to solve the common problem of thermodynamic and kinetic mismatch inherent in the CO2 methanation reaction process, the present invention provides a supported Ni-based catalyst with low raw material price, simple preparation process, easy industrial production, high loading capacity, small metal Ni particle size, high low-temperature CO2 conversion rate and CH4 selectivity, as well as its preparation method and application in low-temperature CO2 methanation reaction.

[0007] The technical solutions adopted to solve the above problems are described below.

[0008] In the first aspect, the present invention provides a supported Ni-based catalyst, wherein the supported Ni-based catalyst comprises a Fe2O3-Al2O3 composite oxide support, a FeNi3 crystal phase and a Ni 0 The Fe2O3-Al2O3 composite oxide has a slit-type mesoporous structure and a specific surface area of ​​300-340 m 2 g -1 , pore volume of 1.0-1.3 cm 3 g -1 , the average pore size is 12-17 nm; according to the X-ray diffraction line width method (Scherrer formula method), the particle size of the FeNi3 crystal phase is 3-10 nm, the Ni 0 The particle size of the crystalline phase is 3-16 nm.

[0009] Preferably, the particle size of the FeNi3 crystal phase is 3-7 nm, more preferably 3-6 nm, and further preferably 3-5 nm.

[0010] Preferably, the specific surface area of ​​the Fe2O3-Al2O3 composite oxide is 300-340 m 2 g -1 , with a pore volume of 1.2-1.3 cm 3 g -1 , with an average pore size of 14-17 nm.

[0011] Preferably, in the Fe2O3-Al2O3 composite oxide, the molar ratio of Fe to Al is 1:3-5, more preferably 1:4.

[0012] Preferably, the Ni loading in the supported Ni-based catalyst is 20-30 wt %. In the present invention, the Ni loading = m Ni / (m Ni +m Fe2O3-Al2O3 )×100%, where m Ni and m Fe2O3-Al2O3 It represents the mass of Ni and the mass of Fe2O3-Al2O3 composite oxide contained in the nickel source (in a specific embodiment, the nickel source is a nickel-containing inorganic salt).

[0013] Preferably, the supported Ni-based catalyst is obtained by using Fe2O3-Al2O3 composite oxide as a carrier, loading nickel-containing inorganic salt by wet impregnation, and then drying, calcining, hydrogen reduction, and passivation.

[0014] As a further preference, the calcination condition is: calcination at 420-470° C. for 4-5 h.

[0015] As a further preference, the hydrogen reduction condition is: performing reduction treatment at 500-600° C. for 1-3 hours under hydrogen atmosphere.

[0016] As a further preference, the passivation conditions are: passivation treatment is carried out at room temperature for 0.5-2 hours under a passivation atmosphere; the passivation atmosphere is a mixed atmosphere of O2 and N2, wherein the volume percentage of oxygen is 0.5-1.5%.

[0017] In the second aspect, the present invention provides a method for preparing the supported Ni-based catalyst described in the first aspect, comprising the following steps: using Fe2O3-Al2O3 composite oxide as a carrier, loading nickel-containing inorganic salt by wet impregnation, and obtaining a supported Ni-based catalyst through drying, calcination, hydrogen reduction, and passivation.

[0018] Preferably, the Fe2O3-Al2O3 composite oxide is prepared by coprecipitation. Further preferably, the Fe2O3-Al2O3 composite oxide is prepared by the following steps:

[0019] Step 1: dissolving an iron-containing inorganic salt and an aluminum-containing inorganic salt in deionized water to obtain a mixed salt solution;

[0020] Step 2: dissolving carbonate in deionized water to obtain a precipitant solution;

[0021] Step 3: Add the mixed salt solution dropwise to the precipitant solution at 90-100°C. After the addition is complete, adjust the pH of the mixed slurry to 7.3-7.5 (preferably 7.4-7.5, more preferably 7.4) using an alkaline solution, and then age the mixture under stirring.

[0022] Step 4: Filter the mixed slurry into a filter cake, and then wash the filter cake thoroughly with deionized water and alcohol solvent in sequence;

[0023] Step 5: Place the filter cake obtained in step 4 into a muffle furnace and calcine to obtain a Fe2O3-Al2O3 oxide carrier.

[0024] In step 1 of the present invention, the molar ratio of Fe to Al in the iron-containing inorganic salt and the aluminum-containing inorganic salt is preferably 1:3-5, more preferably 1:4. The iron-containing inorganic salt and the aluminum-containing inorganic salt are preferably ferric nitrate nonahydrate and aluminum nitrate nonahydrate. The concentrations of ferric nitrate nonahydrate and aluminum nitrate nonahydrate in the mixed salt solution are preferably 0.24-0.48 g cm -3 and 0.68–0.9 g cm -3 .

[0025] In step 2 of the present invention, the carbonate is preferably ammonium carbonate, and the concentration of the carbonate in the precipitant solution is preferably 0.2-0.4 g cm -3 .

[0026] In step 3 of the present invention, the alkaline solution is preferably an aqueous solution of ammonium carbonate, wherein the concentration of ammonium carbonate is 0.07-0.09 g cm -3 , more preferably 0.08 g cm -3 .

[0027] In step 3 of the present invention, the aging time is preferably 10-20 min, most preferably 15 min.

[0028] In step 4 of the present invention, the alcohol solvent is preferably methanol, ethanol or ethylene glycol, preferably ethanol.

[0029] In step 5 of the present invention, the calcination temperature is preferably 500-600 o C, most preferably 550 o C; the calcination time is preferably 2h.

[0030] Preferably, the specific operation of the preparation method of the supported Ni-based catalyst is: dissolving a nickel-containing inorganic salt in deionized water to obtain an impregnation solution; after stirring the impregnation solution evenly, adding a Fe2O3-Al2O3 composite oxide support, stirring at room temperature for 10-14 h, then placing the sample in an oven for drying, and then placing the dried sample in a muffle furnace and calcining at 420-470°C for 4-5 h, and then reducing it at 500-600°C under hydrogen atmosphere for 1-3 h, and then passivating it at room temperature for 0.5-2 h under a passivation atmosphere; the passivation atmosphere is a mixed atmosphere of O2 and N2, in which the volume percentage of oxygen is 0.5-1.5%, to obtain a supported Ni-based catalyst.

[0031] As a further preference, the nickel-containing inorganic salt is nickel nitrate hexahydrate.

[0032] As a further preference, the drying treatment temperature is 90-110°C, more preferably 100°C; the drying treatment time is 3-5 h, more preferably 4 h.

[0033] As a further preference, the calcination temperature is 450°C.

[0034] As a further preference, the reduction treatment temperature is 550° C. and the reduction treatment time is 2 h.

[0035] As a further preference, the passivation conditions are: passivation treatment is carried out at room temperature for 1-2 h under a passivation atmosphere; the passivation atmosphere is a mixed atmosphere of O2 and N2, wherein the volume percentage thereof is 1%.

[0036] In a third aspect, the present invention provides an application of the supported Ni-based catalyst described in the first aspect in a low-temperature CO2 methanation reaction, wherein the low temperature refers to a reaction temperature of the CO2 methanation reaction less than 300°C, and the supported Ni-based catalyst is first reduced with hydrogen before application.

[0037] As a preference, the hydrogen reduction conditions are: the reduction pressure is normal pressure, the H2 flow rate is 65-75 cm 3 min -1 , the reduction temperature is 350-420 ℃, and the treatment time is 0.5-1.5h.

[0038] Compared with the prior art, the present invention has the following advantages: 1) Aiming at the problem that the Ni-based catalyst with Al2O3 as the carrier has poor catalytic performance in the CO2 methanation reaction, the present invention selects Fe2O3-Al2O3 composite oxide with a specific structure as the carrier to prepare the supported Ni-based catalyst. The introduction of Fe2O3 and the structure of the Fe2O3-Al2O3 composite oxide enable the formation of FeNi3 crystal phases and Ni of a certain size in the catalyst. 0 crystalline phase, significantly improving the performance of Ni-based catalysts in low-temperature CO2 methanation reactions. 2) The method for preparing the supported Ni-based catalyst reported in this invention has the advantages of low raw material costs, a simple preparation process, and ease of industrial production. 3) The supported Ni-based catalyst prepared by this invention has the advantages of high loading capacity and small metallic Ni particle size. 4) The Ni-based catalyst prepared by this invention has high low-temperature CO2 methanation reaction activity and methane selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 3 and Comparative Example 1. The low-temperature N2 adsorption-desorption isotherms of the Fe2O3-Al2O3 mixed oxide and Al2O3 materials prepared in Example 1, Example 2, Example 3 and Comparative Example 1.

[0040] Figure 2 is the XRD pattern of the catalyst prepared in Example 4.

[0041] Figure 3 This is the low-temperature N2 adsorption-desorption isotherm of the Fe2O3-Al2O3 mixed oxide prepared in Example 5.

[0042] Figure 4 is the XRD pattern of the catalyst prepared in Example 5. Figure 5 This is the low-temperature N2 adsorption-desorption isotherm of the Fe2O3-Al2O3 mixed oxide prepared in Comparative Example 3.

[0043] Figure 6 Schematic diagram of the reaction performance of the catalysts prepared by Example 4 and Comparative Example 2.

[0044] Figure 7 Schematic diagram of the reaction performance of the catalyst prepared in Comparative Example 3. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited by the following embodiments.

[0046] The sources and prices of some reagents used in the examples of the present invention can be referred to in the following Table 1:

[0047] Table 1

[0048] Item No. sample purity Price (Yuan) brand 80072718-500g Ferric nitrate nonahydrate AR (Shanghai test), ≥98.5% 30 Sinopharm c804687-500g Cerium nitrate hexahydrate 99.95%, metals basis 209.6 Maclean z822551-500g Zirconium nitrate pentahydrate AR, 99.0% 220 Maclean f809609-500g Ferric oxide AR, 99.0% 50.4 Maclean c804513-500g Cerium Dioxide 99.95%, metals basis 420.8 Maclean z805381-500g Zirconium dioxide 99.00% 288.72 Aladdin R003311-500g Aluminum nitrate nonahydrate AR, 99% 47 Ron

[0049] In the examples of the present invention, if the specific conditions are not specified, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are conventional products that can be obtained by conventional techniques or purchased commercially.

[0050] The present invention tests and analyzes the texture (specific surface area, pore volume, average pore diameter) of Fe2O3-Al2O3 mixed oxides through low-temperature N2 physical adsorption-desorption experiments. The instrument used is ASAP-2020 fully automatic specific surface area and pore analyzer (Micromeritics). The specific test process is as follows: First, the sample is heated at 300 o The samples were degassed at 400 °C for 5 h to remove impurity gases and water adsorbed on the sample surface. The degassed samples were then placed in liquid nitrogen for low-temperature physical N adsorption-desorption testing. Adsorption-desorption isotherms were generated and the hysteresis loop shapes were analyzed. The specific surface area was calculated using the BET equation, the pore volume was calculated from the saturated adsorption capacity on the isotherm, and the average pore size was calculated using the 4V / A equation.

[0051] The crystalline phase of the supported Ni-based catalyst in this invention was determined by X-ray diffraction (XRD). The test instrument was a Rigaku Smart Lab SE from Japan. Before testing, the sample was ground into a fine powder and spread flat on a flat plate. XRD analysis was then performed. The test conditions were: a Cu target (Cu Kα, λ = 0.1541 nm) as the X-ray source, an operating voltage of 40 kV, an operating current of 40 mA, a scan rate of 5° / min, and a scan range of 10° to 80°. The grain size was calculated using the Scherrer equation:

[0052]

[0053] Wherein, λ is the wavelength of X-rays, in nm; β is the half-width at half maximum of the diffraction peak, in radians; θ is the Bragg diffraction angle, in degrees; and D is the grain size, in nm.

[0054] Example 1: Preparation of Fe2O3-Al2O3 mixed oxide support (Fe / Al molar ratio = 2 / 8)

[0055] 12.12 g of Fe(NO3)3·9H2O and 45.01 g of Al(NO3)3·9H2O were dissolved in a 50 cm 3 Mixed solution A was obtained in deionized water. 50 g of ammonium carbonate was dissolved in 150 cm 3Solution B was prepared in deionized water. Solution A was added dropwise to solution B under stirring at a water bath temperature of 95°C to obtain a mixed slurry. After the addition was completed, an ammonium carbonate aqueous solution (0.08 g cm -3 ) The pH of the mixed slurry was adjusted to 7.4, and then aged for 15 minutes under stirring. The mixed slurry was filtered to obtain a filter cake, which was then added to deionized water at room temperature and stirred for 30 minutes, and then filtered again; after repeating the above steps three times, the filter cake was added to anhydrous ethanol, stirred at room temperature for 45 minutes, and then filtered. After repeating the above steps twice, the filter cake was filtered again to obtain a filter cake. The obtained filter cake was directly placed in a muffle furnace and calcined (calcination temperature = 550 ° C, calcination time = 2 h) to obtain Fe2O3-Al2O3 composite oxide (Fe / Al molar ratio = 2 / 8, specific surface area = 309.4 m 2 g -1 , pore volume = 1.27 cm 3 g -1 , average pore size = 16.5 nm). Figure 1 As shown in the figure, the adsorption isotherm of the sample is a type IV isotherm, and the hysteresis loop type is H3 type, which indicates that the sample has a slit-type mesoporous structure.

[0056] Example 2: Preparation of Fe2O3-Al2O3 mixed oxide support (Fe / Al molar ratio = 3 / 7)

[0057] 18.18 g of Fe(NO3)3·9H2O and 39.39 g of Al(NO3)3·9H2O were dissolved in a 50 cm 3 Mixed solution A was obtained in deionized water. 50 g of ammonium carbonate was dissolved in 150 cm 3 Solution B was prepared in deionized water. Solution A was added dropwise to solution B under stirring at a water bath temperature of 95°C to obtain a mixed slurry. After the addition was completed, an ammonium carbonate aqueous solution (0.08 g cm -3 ) The pH of the mixed slurry was adjusted to 7.4, and then aged for 15 minutes under stirring. The mixed slurry was filtered to obtain a filter cake, and then the filter cake was added to deionized water at room temperature and stirred for 30 minutes, and then filtered again; after repeating the above steps three times, the filter cake was added to anhydrous ethanol, stirred at room temperature for 45 minutes, and then filtered. After repeating the above steps twice, the filter cake was filtered again to obtain a filter cake. The obtained filter cake was directly placed in a muffle furnace and calcined (calcination temperature = 550 ° C, calcination time = 2 h) to obtain Fe2O3-Al2O3 composite oxide (Fe / Al molar ratio = 3 / 7, specific surface area = 336.5 m 2 g -1, pore volume = 1.02 cm 3 g -1 , average pore size = 12.1 nm). Figure 1 As shown in the figure, the adsorption isotherm of the sample is a type IV isotherm, and the hysteresis loop type is H3 type, which indicates that the sample has a slit-type mesoporous structure.

[0058] Example 3: Preparation of Fe2O3-Al2O3 mixed oxide support (Fe / Al molar ratio = 4 / 6)

[0059] 24.24 g of Fe(NO3)3·9H2O and 33.76 g of Al(NO3)3·9H2O were dissolved in a 50 cm -3 Mixed solution A was obtained in deionized water. 50 g of ammonium carbonate was dissolved in 150 cm -3 Solution B was prepared in deionized water. Solution A was added dropwise to solution B under stirring at a water bath temperature of 95°C to obtain a mixed slurry. After the addition was completed, an ammonium carbonate aqueous solution (0.08 g cm -3 ) The pH of the mixed slurry was adjusted to 7.4, and then aged for 15 minutes under stirring. The mixed slurry was filtered to obtain a filter cake, which was then added to deionized water at room temperature and stirred for 30 minutes, and then filtered again; after repeating the above steps three times, the filter cake was added to anhydrous ethanol, stirred at room temperature for 45 minutes, and then filtered. After repeating the above steps twice, the filter cake was filtered again to obtain a filter cake. The obtained filter cake was directly placed in a muffle furnace and calcined (calcination temperature = 550 ° C, calcination time = 2 h) to obtain Fe2O3-Al2O3 composite oxide (Fe / Al molar ratio = 4 / 6, specific surface area = 300.4 m 2 g -1 , pore volume = 1.04 cm 3 g -1 , average pore size = 13.9 nm). Figure 1 As shown, the adsorption isotherm of the sample is a type IV isotherm, and the hysteresis loop type is H3 type, indicating that the sample has a slit-type mesoporous structure.

[0060] Example 4: Fe2O3-Al2O3 mixed oxide supported Ni-based catalyst (Ni = 20 wt%)

[0061] Weigh 2.477 g Ni(NO3)2·6H2O and dissolve it in 20 cm -32 g of the Fe2O3-Al2O3 composite oxide supports with different Fe / Al molar ratios prepared in Examples 1, 2, and 3 were added to deionized water and stirred for 12 h to obtain a mixture. The mixture was then dried in an oven at 100°C for 4 h. The dried sample was placed in a muffle furnace and calcined at 450°C for 5 h. The calcined product was subjected to a reduction pretreatment (reduction temperature = 550°C) under H2 atmosphere. o C, reduction time = 2h), and then the above-mentioned reduction product was passivated at room temperature (passivation atmosphere: 1% O2 / N2, passivation time: 1h) to obtain Fe2O3-Al2O3 supported Ni catalyst (Ni = 20wt%, Fe / Al molar ratios of 2 / 8, 3 / 7 and 4 / 6, respectively), and the catalyst was characterized by XRD. Figure 2 This is the XRD pattern of a Ni-based catalyst after reduction / passivation treatment. The diffraction peaks at 2θ ≈ 37° and 66° are attributed to γ-Al2O3 (PDF#29-0063). A broad peak at 2θ ≈ 44-45°, consisting of two overlapping peaks, is significantly more intense than the other diffraction peaks. Peak fitting using the Scherrer equation indicates that the peak at 2θ ≈ 44° can be attributed to the FeNi3 crystalline phase (PDF#38-0419). The intensity of this peak increases with increasing iron content in the catalyst support. The particle sizes for Ni / Fe2O3-Al2O3 (Fe / Al=2 / 8) are as follows: 4.8 nm for Ni / Fe2O3-Al2O3 (Fe / Al=3 / 7) = 7.1 nm for Ni / Fe2O3-Al2O3 (Fe / Al=4 / 6) = 8.4 nm. The diffraction peak at 2θ ≈ 44.4° can be attributed to Ni 0 Crystalline phase (PDF# 87-0712), and the order of particle size from small to large is: Ni / Fe2O3-Al2O3(Fe / Al=2 / 8) = 3.5 nm < Ni / Fe2O3-Al2O3(Fe / Al=3 / 7) = 9.2 nm < Ni / Fe2O3-Al2O3(Fe / Al=4 / 6) = 10 nm. Therefore, as the iron content in the Fe2O3-Al2O3 mixed oxide supported Ni-based catalyst increases, the Ni content in the catalyst increases. 0 And the FeNi3 grain size gradually increases.

[0062] Example 5: Fe2O3-Al2O3 mixed oxide carrier supported Ni-based catalyst (Ni = 26 wt%)

[0063] 12.11 g of Fe(NO3)3·9H2O and 45.01 g of Al(NO3)3·9H2O were dissolved in a 50 cm 3 Mixed solution A was obtained in deionized water. 34.57 g of ammonium carbonate was dissolved in 150 cm 3 Solution B was prepared in deionized water. Solution A was added dropwise to Solution B in a water bath at 95°C with stirring to obtain a mixed slurry. After the addition, the pH of the mixed slurry was adjusted to 7.4 using the aforementioned aqueous ammonium carbonate solution and then aged for 15 minutes under stirring. The mixed slurry was filtered to obtain a filter cake, which was then added to deionized water at room temperature, stirred for 30 minutes, and filtered again. This step was repeated three times, and the filter cake was added to anhydrous ethanol, stirred at room temperature for 25 minutes, and filtered again. This step was repeated two more times, and the filter cake was filtered again to obtain a filter cake. The resulting filter cake was directly calcined in a muffle furnace (calcination temperature = 550°C, calcination time = 2 h) to obtain an Fe2O3-Al2O3 composite oxide (Fe / Al molar ratio = 2 / 8, specific surface area = 335.2 m2). 2 g -1 , pore volume = 1.25 cm 3 g -1 , average pore size = 14.9 nm). Figure 3 As shown in the figure, the adsorption isotherm of the sample is a type IV isotherm, and the hysteresis loop type is H3 type, which indicates that the sample has a slit-type mesoporous structure.

[0064] Weigh 5.1 g Ni(NO3)2·6H2O and dissolve it in 20 cm -3 Then, 3 g of the Fe2O3-Al2O3 (Fe / Al molar ratio = 2 / 8) composite oxide support was added to deionized water and stirred for 12 h to obtain a mixture. The mixture was then placed in an oven at 100 °C for 4 h. The dried sample was placed in a muffle furnace and calcined at 450 °C for 4 h. The calcined product was subjected to reduction pretreatment (reduction temperature = 550 °C) under H2 atmosphere. o C, reduction time = 2h), and then the above-mentioned reduction product was passivated at room temperature (passivation atmosphere: 1% O2 / N2, passivation time: 2h) to obtain Fe2O3-Al2O3 supported Ni catalyst (Ni = 26wt%, Fe / Al molar ratio: 2 / 8), and the catalyst was characterized by XRD. Figure 4This is the XRD pattern of the Ni-based catalyst after passivation treatment. The XRD characterization results show that the sample also has a broad peak at 2θ ≈ 44-45°, which is composed of two overlapping peaks and has an intensity significantly higher than other diffraction peaks. The peak fitting estimation is performed using the Scherrer equation, where the peak at 2θ ≈ 44° can be attributed to the FeNi3 crystal phase (PDF#38-0419), with a particle size of 3.6 nm. The peak at 2θ ≈ 44.4° can be attributed to the Ni 0 Crystalline phase (PDF# 87-0712), with a particle size of 15.5 nm.

[0065] Comparative Example 1: Al2O3 carrier

[0066] 56.3 g of Al(NO3)3·9H2O was dissolved in 50 cm -3 Solution A was obtained in deionized water. 50 g of ammonium carbonate was dissolved in 150 cm -3 Solution B was prepared in deionized water. Solution A was added dropwise to solution B under stirring at a water bath temperature of 95°C to obtain a mixed slurry. After the addition was completed, an ammonium carbonate aqueous solution (0.08 g cm -3 ) The pH of the mixed slurry was adjusted to 7.4, and then aged for 15 minutes under stirring. The mixed slurry was filtered to obtain a filter cake, and then the filter cake was added to deionized water at room temperature and stirred for 30 minutes, and then filtered again; after repeating the above steps three times, the filter cake was added to anhydrous ethanol, stirred at room temperature for 45 minutes and then filtered, and the above steps were repeated twice to obtain a filter cake by filtration again. The obtained filter cake was directly placed in a muffle furnace and calcined (calcination temperature = 550 ° C, calcination time = 2 h) to obtain Al2O3 material (specific surface area = 330.2 m 2 g -1 , pore volume = 1.13 cm 3 g -1 , average pore size = 13.7 nm). Figure 1 As shown in FIG, the adsorption isotherm of the sample is a type IV isotherm, and the hysteresis loop type is H3 type, indicating that the sample has a slit-type mesoporous structure. By comparing Examples 1, 2, and 3 with Comparative Example 1, it can be found that the preparation method reported in the present invention can be used to prepare a sample with a high specific surface area (>300 m2) within a certain iron content range. 2 g -1 ), Fe2O3-Al2O3 mixed oxides with large pore volume and average pore diameter and a slit-type mesoporous structure. At the same time, adding a certain amount of iron oxide to alumina does not significantly change the textural properties of the oxide.

[0067] Comparative Example 2: Al2O3-supported Ni-based catalyst (Ni = 20 wt%)

[0068] Weigh 2.477 g Ni(NO3)2·6H2O and dissolve it in 20 cm -3 2 g of the Al2O3 carrier prepared in Comparative Example 1 was added to deionized water and stirred for 12 h to obtain a mixture. The mixture was then placed in an oven at 100°C for 4 h. The dried sample was placed in a muffle furnace and calcined at 450°C for 5 h. The calcined product was subjected to reduction pretreatment under H2 atmosphere (reduction temperature = 550 o C, reduction time = 2h), and then the above reduction product was passivated at room temperature (passivation atmosphere was 1% O2 / N2, passivation time was 1h) to obtain Al2O3 supported Ni catalyst (Ni = 20wt%), and then the catalyst was characterized by XRD. The XRD characterization results showed that ( Figure 2 ), this sample also has a broad peak at 2θ ≈ 44-45°, which is composed of two overlapping peaks and has a significantly higher intensity than other diffraction peaks. Using the Scherrer equation to estimate the peaks, the peak at 2θ ≈ 45.7° can be attributed to γ-Al2O3 (PDF#29-0063). The peak at 2θ ≈ 44.4° can be attributed to Ni 0 Crystal phase (PDF# 87-0712), its particle size is 3.5 nm. By comparing Example 4 with Comparative Example 2, it can be found that the supported Ni-based catalyst prepared by using Fe2O3-Al2O3 mixed oxide as the carrier will form FeNi3 and Ni after the reduction pretreatment of the present invention. 0 On the γ-Al2O3 support, only Ni 0 Crystal phase. When the iron content in the Fe2O3-Al2O3 mixed oxide carrier is low (Fe / Al=2 / 8), the Ni 0 The particle size (3.5 nm) is similar to that of γ-Al2O3 supported Ni-based catalyst (3.5 nm). Further increasing the iron content in the Fe2O3-Al2O3 mixed oxide support will weaken the metal-oxide support interaction, making its Ni 0 and FeNi3 grain growth.

[0069] Comparative Example 3: Fe2O3-Al2O3 supported Ni-based catalyst (Ni = 20wt%)

[0070] 12.12 g of Fe(NO3)3·9H2O and 45.01 g of Al(NO3)3·9H2O were dissolved in a 50 cm 3 Mixed solution A was obtained in deionized water. 34.59 g of ammonium carbonate was dissolved in 150 cm 3Solution B was prepared in deionized water. Solution A was added dropwise to solution B under stirring at a water bath temperature of 95°C to obtain a mixed slurry. After the addition was completed, an ammonium carbonate aqueous solution (0.1 g cm -3 ) The pH of the mixed slurry was adjusted to 7.2, and then aged for 10 minutes under static conditions. The mixed slurry was filtered to obtain a filter cake, which was then added to deionized water at room temperature and stirred for 30 minutes, and then filtered again; after repeating the above steps three times, the filter cake was added to anhydrous ethanol, stirred at room temperature for 30 minutes, and then filtered. After repeating the above steps twice, the filter cake was filtered again to obtain a filter cake. The obtained filter cake was directly placed in a muffle furnace and calcined (calcination temperature = 550°C, calcination time = 2 h) to obtain Fe2O3-Al2O3 composite oxide (Fe / Al molar ratio = 2 / 8, specific surface area = 265.7 m 2 g -1 , pore volume = 1.27 cm 3 g -1 , average pore size = 19.1 nm). Figure 5 As shown, the adsorption isotherm of the sample is a type IV isotherm, but the hysteresis loop type is closer to the H1 type, indicating that the mesoporous structure of the sample is different from that of Examples 1 and 5.

[0071] Weigh 2.477 g Ni(NO3)2·6H2O and dissolve it in 20 cm -3 Then, 2 g of the Fe2O3-Al2O3 composite oxide support prepared above was added to deionized water and stirred for 12 h to obtain a mixture. The mixture was then placed in an oven at 100°C for 4 h. The dried sample was placed in a muffle furnace and calcined at 450°C for 5 h. The calcined product was subjected to reduction pretreatment under H2 atmosphere (reduction temperature = 550 o C, reduction time = 2h), and then the above-mentioned reduction product was passivated at room temperature (passivation atmosphere: 1% O2 / N2, passivation time: 1h) to obtain Fe2O3-Al2O3 supported Ni catalyst (Ni = 20wt%, Fe / Al molar ratio: 2 / 8).

[0072] Example 6

[0073] The catalyst's CO2 methanation performance was evaluated using a fixed-bed reactor. 0.25 g of the catalysts (40-60 mesh) prepared in Example 4, Comparative Example 2, and Comparative Example 3 were diluted with SiO2 diluent at a mass ratio of 1 / 2 and then directly loaded into the constant temperature zone of the reaction tube. Prior to the reaction, the catalyst was again reduced (at atmospheric pressure and a H2 flow rate of 70 cm / s). 3 min-1 , reduction temperature was 400 °C, and treatment time was 1 h). After the reduction treatment, the CO2 methanation reaction performance of the catalyst was evaluated under the following conditions: CO2 / H2 / N2=18:72:10; P=1 MPa; T=250 o C; Mixed gas flow rate = 100 cm 3 min -1 The liquid products after the reaction were collected in a cold trap, and the gaseous products were analyzed using a Shimadzu gas chromatograph (GC-2014ATF). H₂, CO, CO₂, CH₄, and N₂ were separated using a TDX-01 packed column and analyzed using a thermal conductivity detector (TCD), with N₂ as the internal standard.

[0074] The calculation formulas for CO2 conversion and CH4 selectivity are as follows:

[0075] (1-1)

[0076] In the above formula: -X represents the conversion rate, in is the air inlet, and out is the air outlet.

[0077] (1-2)

[0078] In the above formula: -S represents selectivity, in is the air inlet, and out is the air outlet.

[0079] Figure 6 The CO2 methanation reaction performance diagram of the catalyst prepared by the method described in Example 4 and Comparative Example 2 is shown in the figure. o Under reaction conditions of 100 ℃, the Fe2O3-Al2O3 mixed oxide-supported Ni-based catalyst prepared by the method of the present invention exhibited superior CH4 selectivity (> 97%) and reaction stability to the γ-Al2O3-supported Ni-based catalyst. Furthermore, when the Fe / Al ratio in the Fe2O3-Al2O3 mixed oxide support was 2 / 8, the CO2 conversion rate of the catalyst was much higher than that of the γ-Al2O3-supported Ni-based catalyst. Figure 7 This graph shows the CO2 methanation performance of the catalyst prepared by the method described in Comparative Example 3. A comparison of Example 4 and Comparative Example 3 demonstrates that the mesoporous structure of the support affects the structure and performance of the catalyst. The use of the Fe2O3-Al2O3 mixed oxide of the present invention, which possesses a specific surface area, pore volume, and average pore diameter, and a slit-type mesoporous structure, is crucial for controlling the catalyst's structure and performance.

[0080] Example 7

[0081] 0.2 g of the catalyst prepared in Example 5 (40-60 mesh) was diluted with 0.2 g of SiO2 diluent and then directly loaded into the constant temperature zone of the reaction tube. Before the reaction, the catalyst was reduced again (reduction pressure was normal pressure, H2 flow rate was 70 cm 3 min -1 , reduction temperature was 400 °C, and treatment time was 1 h). After the reduction treatment, the CO2 methanation reaction performance of the catalyst was evaluated under the following conditions: CO2 / H2 / N2=18:72:10; P=1 MPa; T=250 o C; Mixed gas flow rate = 100cm 3 min -1 The liquid products after the reaction were collected in a cold trap, and the gaseous products were analyzed using a Shimadzu gas chromatograph (GC-2014ATF). H₂, CO, CO₂, CH₄, and N₂ were separated using a TDX-01 packed column and analyzed using a thermal conductivity detector (TCD), with N₂ as the internal standard.

[0082] The results show that when the metal Ni loading is further increased to 26%, the CO2 conversion rate of the Fe2O3-Al2O3 (Fe / Al=2 / 8) supported Ni-based catalyst can be further increased to 75%, and the CH4 selectivity remains at 99%.

[0083] Moreover, as can be seen from Table 1, compared with using ZrO2 and CeO2 as carriers, the use of Fe2O3-Al2O3 mixed oxides as carriers to prepare supported Ni-based catalysts in the present invention can significantly reduce production costs, thereby facilitating large-scale production of catalysts and the commercial application and promotion of low-temperature CO2 methanation processes.

Claims

1. A supported Ni-based catalyst, characterized in that: The supported Ni-based catalyst comprises a Fe2O3-Al2O3 composite oxide carrier, a FeNi3 crystal phase and a Ni 0 The Fe2O3-Al2O3 composite oxide carrier has a slit-type mesoporous structure and a specific surface area of ​​300-340 m 2 g -1 , pore volume of 1.0-1.3 cm 3 g -1 , the average pore size is 12-17 nm; according to the X-ray diffraction line width method, the particle size of the FeNi3 crystal phase is 3-10 nm, the Ni 0 The particle size of the crystalline phase is 3-16 nm; in the Fe2O3-Al2O3 composite oxide, the molar ratio of Fe and Al is 1:3-5; in the supported Ni-based catalyst, the Ni loading is 20-30wt%.

2. The supported Ni-based catalyst according to claim 1, wherein: The particle size of the FeNi3 crystal phase is 3-7 nm.

3. The supported Ni-based catalyst according to claim 2, wherein: The particle size of the FeNi3 crystal phase is 3-6 nm.

4. The supported Ni-based catalyst according to claim 3, wherein: The particle size of the FeNi3 crystal phase is 3-5 nm.

5. The supported Ni-based catalyst according to any one of claims 1 to 4, wherein: In the Fe2O3-Al2O3 composite oxide, the molar ratio of Fe to Al is 1:

4.

6. A method for preparing a supported Ni-based catalyst as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: using Fe2O3-Al2O3 composite oxide as a carrier, loading nickel-containing inorganic salt by wet impregnation, and obtaining a supported Ni-based catalyst through drying, roasting, hydrogen reduction, and passivation.

7. The preparation method according to claim 6, wherein: The Fe2O3-Al2O3 composite oxide is prepared by the following steps: Step 1: dissolving an iron-containing inorganic salt and an aluminum-containing inorganic salt in deionized water to obtain a mixed salt solution; Step 2: dissolving carbonate in deionized water to obtain a precipitant solution; Step 3: Add the mixed salt solution dropwise to the precipitant solution at 90-100°C. After the addition is complete, adjust the pH of the mixed slurry to 7.3-7.5 with an alkaline solution, and then age the mixture under stirring. Step 4: Filter the mixed slurry into a filter cake, and then wash the filter cake thoroughly with deionized water and alcohol solvent in sequence; Step 5: Place the filter cake obtained in step 4 into a muffle furnace and calcine to obtain a Fe2O3-Al2O3 oxide carrier.

8. The preparation method according to claim 7, wherein: In step 3, the aging time is 10-20 min; in step 5, the calcination temperature is 500-600 o C.

9. The preparation method according to claim 6, wherein: The specific operation of the preparation method of the supported Ni-based catalyst is as follows: dissolving a nickel-containing inorganic salt in deionized water to obtain an impregnation solution; after stirring the impregnation solution evenly, adding a Fe2O3-Al2O3 composite oxide support, stirring at room temperature for 10-14 hours, then placing the sample in an oven for drying, and then placing the dried sample in a muffle furnace for calcining at 420-470°C for 4-5 hours, and then performing a reduction treatment at 500-600°C under hydrogen atmosphere for 1-3 hours, and then performing a passivation treatment at room temperature for 0.5-2 hours under a passivation atmosphere; the passivation atmosphere is a mixed atmosphere of O2 and N2, wherein the volume percentage of oxygen is 0.5-1.5%, to obtain a supported Ni-based catalyst.

10. Use of the supported Ni-based catalyst according to any one of claims 1 to 5 in a low-temperature CO2 methanation reaction, wherein the low temperature refers to a reaction temperature of the CO2 methanation reaction of less than 300°C, and the supported Ni-based catalyst is first reduced with hydrogen before use.

11. The use according to claim 10, characterized in that: The hydrogen reduction conditions are: the reduction pressure is normal pressure, the H2 flow rate is 65-75 cm 3 min -1 , the reduction temperature is 350-420 ℃, and the treatment time is 0.5-1.5h.

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