Mg-Fe-Ag composite hydrogenation catalyst, preparation method and application thereof

Abstract

This invention relates to the field of catalyst technology, and discloses a Mg-Fe-Ag composite hydrogenation catalyst, its preparation method, and its application. The Mg-Fe-Ag composite hydrogenation catalyst comprises Mg-Fe modified graphite; the Mg-Fe modified graphite comprises a graphite support, and iron oxide and magnesium oxide supported on the graphite support; the iron oxide is doped with Ag. + The Mg-Fe modified graphite has Ag loaded on its surface. + And the interlayer load has Ag 0 The catalyst of this invention can achieve higher CO2 conversion and olefin selectivity when used in the catalytic reaction of CO2 hydrogenation to olefins.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a Mg-Fe-Ag composite hydrogenation catalyst, its preparation method, and its application. Background Technology

[0002] The hydrogenation of CO2 to olefins is mainly divided into indirect and direct methods. The indirect method, also known as the methanol route, involves first converting CO2 into methanol and other oxygen-containing compounds, followed by further dehydration to form olefins. The direct method, also known as the Fischer-Tropsch synthesis route, involves first generating CO from CO via reverse water-gas shift (RWGS), followed by Fischer-Tropsch synthesis (FT) to form olefins. Compared to the methanol route, the Fischer-Tropsch synthesis route has a more direct reaction path and is currently the mainstream research direction.

[0003] Fe-based catalysts have good RWGS and FT reaction activity and are one of the commonly used catalysts in the Fischer-Tropsch synthesis route. They have the advantages of low cost and environmental friendliness. However, traditional Fe-based catalysts have weak catalytic activity, low CO2 conversion rate, insufficient olefin selectivity, and are prone to generating by-products such as methane.

[0004] Patent CN120885218A discloses a method for preparing and applying a catalyst for the hydrogenation of carbon dioxide to olefins. This catalyst employs a co-precipitation followed by calcination method, loading Fe and Mg elements onto graphite. By adding Mg to the iron-based catalyst, more low-coordinate Fe atoms are generated, thereby improving the catalyst's catalytic activity. Simultaneously, the electron cloud density of Fe atoms is altered, thus improving olefin selectivity. Furthermore, the support is hydrophobically modified to reduce contact between the active sites and water generated during the reaction, thereby improving the catalyst's stability. However, when used in the CO2 hydrogenation to olefins reaction, the catalyst still suffers from low CO2 conversion and olefin selectivity (the test results described in the patent show that the highest CO2 conversion rate is only 37.46%, and the highest total olefin selectivity is only 72.63%). Summary of the Invention

[0005] To address the technical problem of low CO2 conversion and olefin selectivity in existing iron-based catalysts used in CO2 hydrogenation to olefins, this invention provides a Mg-Fe-Ag composite hydrogenation catalyst that achieves higher CO2 conversion and olefin selectivity when used in catalytic CO2 hydrogenation to olefins.

[0006] The specific technical solution of this invention is as follows: In a first aspect, the present invention provides a Mg-Fe-Ag composite hydrogenation catalyst, comprising Mg-Fe modified graphite; the Mg-Fe modified graphite comprising a graphite support, and iron oxide and magnesium oxide supported on the graphite support; the iron oxide being doped with Ag. + The Mg-Fe modified graphite has Ag loaded on its surface. + And the interlayer load has Ag 0 .

[0007] This invention, based on Mg-Fe modified graphite, introduces Ag at specific locations. + and Ag 0 This can improve the CO2 conversion and olefin selectivity of the catalyst in the CO2 hydrogenation to olefins reaction, specifically by doping Ag into iron oxides. + This can distort its crystal lattice, generating oxygen vacancies and surface defects, becoming active centers for catalytic reactions, improving the efficiency of CO2 hydrogenation to olefins, and thus increasing CO2 conversion; Ag distributed on the surface of Mg-Fe modified graphite + It can suppress methanation side reaction sites during CO2 hydrogenation, thereby reducing the formation of methane byproduct and improving olefin selectivity; Ag supported between Mg-Fe modified graphite layers 0 It can serve as a CO adsorption and activation site, further improving reaction efficiency; and Ag + and Ag 0 This differentiated spatial distribution can also promote in-plane and interlayer charge transport, thus facilitating catalytic reactions.

[0008] In addition, Ag + and Ag 0 The introduction of Ag will not disrupt the distribution of active sites in Mg-Fe modified graphite, thus avoiding an excessive influence on the effect of Mg (which generates more low-coordinate Fe atoms in the catalyst, thereby improving the catalyst's catalytic activity and changing the electron cloud density of Fe atoms, thereby improving olefin selectivity); when the graphite support used is a hydrophobic graphite support, Ag + and Ag 0 The introduction of [the catalyst] will not damage the hydrophobic structure of the support, and can maintain good stability of the catalyst.

[0009] Preferably, the graphite support is a hydrophobic graphite support doped with nitrogen atoms.

[0010] Preferably, the graphite carrier is also loaded with alkali metal elements.

[0011] Secondly, the present invention provides a method for preparing the Mg-Fe-Ag composite hydrogenation catalyst, comprising the following steps: S1: Containing Mg2+ and Fe 3+ The solution and the precipitant solution were added dropwise to the graphite carrier dispersion to carry out a precipitation reaction, and the product was separated. S2: Disperse the product of S1 in water, add Ag-containing... + After the solution reaches adsorption equilibrium, a reducing agent is added to initiate a reduction reaction, causing some Ag to be released. + Convert to Ag 0 Dry and calcine.

[0012] In step S2 above, Ag is adsorbed. + → Part of Ag + Restored to Ag 0 → Calcination not only allows Ag to be incorporated into the resulting iron oxide lattice, but also + It can also make the Ag element on the catalyst surface mainly Ag + The form exists, and Ag exists between layers. 0 The specific mechanism is as follows: During the synthesis of the catalyst, Ag... + and Ag 0 The diffusion rates of species on the catalyst surface differ. Ag + Ag typically has higher migration ability and is more likely to "preempt" some active sites, thus preemptively and stably bonding to the catalyst surface. 0 These exist in atomic or cluster form, migrating relatively slowly, ultimately leading to differences in spatial distribution. Furthermore, during catalyst synthesis, hydroxyl groups on the catalyst surface readily anchor Ag. + Stable Ag-O-support bonds are formed, therefore the Ag element on the catalyst surface mainly exists as Ag. + It exists in form, Ag 0 They tend to be distributed between layers.

[0013] Preferably, in step S2, the reducing agent is NaBH4 or Ag. + The mass ratio of NaBH4 to NaBH4 is 1:0.1~1, the reduction reaction temperature is 20~25℃, and the time is 10~15 min; or, the reducing agent is ascorbic acid, Ag + The mass ratio of ascorbic acid to ascorbic acid is 1:1~2, the temperature of the reduction reaction is 20~60℃, and the time is 1~4 h.

[0014] Preferably, in step S1, the Mg 2+ with Fe 3+ The molar ratio of the graphite carrier and Fe is 1:1.5~2.5. 3+ The mass ratio is 1:0.2~0.7; in step S2, the Ag... + The dosage is 0.5~1.5 wt% of the S1 product, wherein the Ag-containing product... +Ag in solution + The content is 0.001~0.005 g / mL, with the addition of Ag. + The solution flow rate is 1-3 mL / min, and the adsorption equilibrium time is 20-40 min. Preferably, in step S2, the drying temperature is 40-60℃; the calcination process is carried out in an inert atmosphere at a temperature of 500-600℃ for 2-6 h.

[0015] Preferably, before step S1, the graphite support is hydrophobically modified and doped with nitrogen atoms. The specific process includes: dispersing the graphite support in a mixture of dodecane and hexadecane, stirring it evenly, stirring it at 200~300℃ for 4~24 h, separating the product, mixing it with urea and ball milling it, and calcining it at 300~350℃ for 3.5~4.5 h in an inert atmosphere.

[0016] Preferably, before step S2, an alkali metal element is loaded onto the product S1. The specific process includes: adding the product S1 into a solution containing alkali metal ions, ultrasonically treating it, and then drying it.

[0017] Thirdly, the present invention provides the application of the Mg-Fe-Ag composite hydrogenation catalyst in the catalytic hydrogenation of CO2 to olefins.

[0018] Preferably, during the CO2 hydrogenation to olefins reaction, the temperature is 300~350℃, the volume ratio of H2 to CO2 is 2.5~3.5:1, and the flow rate of the H2 and CO2 mixture is 20~30 mL / min.

[0019] Compared with the prior art, the present invention has the following advantages: (1) In the Mg-Fe-Ag composite hydrogenation catalyst of the present invention, Ag is introduced at specific positions of Mg-Fe modified graphite. + and Ag 0 (Ag doping in iron oxide) + Mg-Fe modified graphite has Ag loaded on its surface. + The interlayer loading of Mg-Fe modified graphite contains Ag. 0 This allows it to achieve higher CO2 conversion and olefin selectivity when used in the catalytic hydrogenation of CO2 to olefins.

[0020] (2) In the process of preparing the Mg-Fe-Ag composite hydrogenation catalyst, the present invention uses Ag adsorption. + → Part of Ag + Restored to Ag 0 → Calcination not only allows Ag to be incorporated into the resulting iron oxide lattice, but also +It can also make the Ag element on the catalyst surface mainly Ag + It exists in form, and Ag is distributed between layers. 0 Thus utilizing Ag + and Ag 0 Its specific location distribution improves CO2 conversion and olefin selectivity. Attached Figure Description

[0021] Figure 1 The composition of alkanes and olefins in the product of the catalyst used in Example 1 during the catalytic hydrogenation of CO2 to olefins.

[0022] Figure 2 The image shows the change in CO2 conversion rate of the catalyst in Example 1 during continuous use.

[0023] Figure 3 The X-ray photoelectron spectroscopy (XPS) spectrum of the catalyst after the stability test in Test Example 2.

[0024] Figure 4 XPS image of the catalyst after etching for 1 min to complete the stability test in Test Example 2.

[0025] Figure 5 X-ray diffraction (XRD) pattern of the catalyst after the stability test in Test Example 2. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] First, this invention relates to a Mg-Fe-Ag composite hydrogenation catalyst, comprising Mg-Fe modified graphite; the Mg-Fe modified graphite includes a graphite support, and iron oxide and magnesium oxide supported on the graphite support; the iron oxide is doped with Ag. + The Mg-Fe modified graphite has Ag loaded on its surface. + And the interlayer load has Ag 0 .

[0028] In some specific embodiments, the graphite support is a hydrophobic graphite support doped with nitrogen atoms.

[0029] In some specific embodiments, the graphite support is further loaded with an alkali metal element. Optionally or preferably, the alkali metal element is sodium (Na).

[0030] In some specific embodiments, the graphite carrier is graphite powder.

[0031] Second, the present invention relates to a method for preparing the Mg-Fe-Ag composite hydrogenation catalyst, the steps of which include: S1: Containing Mg 2+ and Fe 3+ The solution and the precipitant solution were added dropwise to the graphite carrier dispersion to carry out a precipitation reaction, and the product was separated. S2: Disperse the product of S1 in water, add Ag-containing... + After the solution reaches adsorption equilibrium, a reducing agent is added to initiate a reduction reaction, causing some Ag to be released. + Convert to Ag 0 Dry and calcine.

[0032] In some specific embodiments, prior to step S1, the graphite support is hydrophobically modified and doped with nitrogen atoms. The specific process includes: dispersing the graphite support in a mixture of dodecane and hexadecane, stirring thoroughly, and then stirring at 200-300°C for 4-24 h. After separating the product, it is mixed with urea and ball-milled, and then calcined at 300-350°C for 3.5-4.5 h in an inert atmosphere. Optionally or preferably, the mass ratio of dodecane to hexadecane is 1:1-3; the mass ratio of the graphite support to the total mass of dodecane and hexadecane is 1:2-5; the mass ratio of the graphite support to urea is 1:0.3-0.6; and the ball milling speed is 400-700 r / min for 180-250 min.

[0033] In some specific embodiments, in step S1, the Mg 2+ with Fe 3+ The molar ratio of the graphite carrier and Fe is 1:1.5~2.5. 3+ The mass ratio is 1:0.2~0.7.

[0034] In some specific embodiments, in step S1, the precipitant is sodium carbonate.

[0035] In some specific embodiments, in step S1, the method for separating the product is vacuum filtration; after separating the product, it is dried and ground.

[0036] In some specific embodiments, before step S2, an alkali metal element is loaded onto the product of S1. The specific process includes: adding the product of S1 to a solution containing alkali metal ions, ultrasonicating, and then drying. Optionally or preferably, the solute in the solution containing alkali metal ions is one or more of sodium acetate, sodium carbonate, and sodium nitrate.

[0037] In some specific embodiments, in step S2, the reducing agent is NaBH4, Ag + The mass ratio of NaBH4 to NaBH4 is 1:0.1~1, the reduction reaction temperature is 20~25℃, and the time is 10~15 min. In some other specific embodiments, in step S2, the reducing agent is ascorbic acid, Ag+ The mass ratio of ascorbic acid to ascorbic acid is 1:1~2, the temperature of the reduction reaction is 20~60℃, and the time is 1~4 h.

[0038] In some specific embodiments, in step S2, the Ag + The dosage is 0.5~1.5 wt% of the S1 product, wherein the Ag-containing product... + Ag in solution + The content is 0.001~0.005 g / mL, with the addition of Ag. + The solution flow rate is 1-3 mL / min, and the adsorption equilibrium time is 20-40 min. In some specific embodiments, the drying temperature in step S2 is 40-60°C.

[0039] In some specific embodiments, in step S2, the calcination process is carried out in an inert atmosphere at a temperature of 500~600℃ for 2~6 hours.

[0040] Third, the present invention relates to the application of the Mg-Fe-Ag composite hydrogenation catalyst in the catalytic hydrogenation of CO2 to olefins.

[0041] In some specific embodiments, during the CO2 hydrogenation to olefins reaction, the temperature is 300~350℃, the volume ratio of H2 to CO2 is 2.5~3.5:1, and the flow rate of the H2 and CO2 mixture is 20~30 mL / min.

[0042] The present invention will now be described through specific embodiments and comparative examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0043] Example 1: Preparation of Mg-Fe-Ag composite hydrogenation catalyst This embodiment prepares the Mg-Fe-Ag composite hydrogenation catalyst according to the following steps: S1: Preparation of nitrogen-doped hydrophobic graphite carriers 20 g of graphite powder was dispersed in a mixture of 20 g of dodecane and 20 g of hexadecane. After stirring evenly, the mixture was transferred to a hydrothermal reactor and stirred at 220 °C for 8 h. After filtration, washing, and drying, the mixture was mixed with 10 g of urea and ball-milled at 400 r / min for 3 h in a planetary ball mill. Subsequently, the mixture was calcined at 500 °C for 4 h under nitrogen atmosphere to obtain nitrogen-doped hydrophobic graphite support.

[0044] S2: Loaded with insoluble Mg and Fe species Weigh 16.11 g of ferric nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate, dissolve them in deionized water, and prepare Fe... 3+ and Mg2+ A 1.0 mol / L metal salt solution was prepared. Sodium carbonate was dissolved in deionized water to prepare a 1.0 mol / L sodium carbonate solution. 6.464 g of nitrogen-doped hydrophobic graphite support was mixed with 100 mL of deionized water to form a suspension. The metal salt solution and sodium carbonate solution were added dropwise in a parallel stream to induce a precipitation reaction. During the precipitation, the pH was controlled to 8 by adjusting the dropwise rates of solutions A and B, and the temperature was maintained at 60℃ for 30 min. After the precipitation reaction was complete, the mixture was allowed to stand for 2 h, filtered five times, dried at 120℃, and ground to obtain the catalyst precursor powder.

[0045] S3: Loaded with alkali metal elements Take 1 g of catalyst precursor powder and add it to 5 mL of sodium carbonate aqueous solution with a concentration of 0.0092 g / mL. After sonication for 2 h, dry at 120℃ to obtain modified precursor powder.

[0046] S4: Load Ag + and Ag 0 Weigh 0.01 g of silver nitrate and dissolve it in deionized water to prepare a silver nitrate solution with a concentration of 0.001 g / mL. Weigh 0.01 g of NaBH4 and dissolve it in deionized water to prepare a NaBH4 solution with a concentration of 0.001 g / mL. Mix all the modified precursor powder obtained in step S3 with 30 mL of deionized water. At 10 °C, add silver nitrate solution dropwise at a rate of 1 mL / min. After the addition is complete, continue stirring for 30 min to allow adsorption equilibrium to be reached. Then, add 1 mL of NaBH4 solution and stir for 10 min. Dry at 40 °C to obtain the silver-loaded precursor powder.

[0047] S5: Calcination and Post-processing The silver-loaded precursor powder was calcined at 550℃ for 4 h under nitrogen atmosphere, cooled, pressed into tablets at 10 MPa, crushed, and sieved to obtain 40-60 mesh particles, thus obtaining the Mg-Fe-Ag composite hydrogenation catalyst.

[0048] Example 2: Preparation of Mg-Fe-Ag composite hydrogenation catalyst This embodiment prepares the Mg-Fe-Ag composite hydrogenation catalyst according to the following steps: S1: Preparation of nitrogen-doped hydrophobic graphite carriers 20 g of graphite powder was dispersed in a mixture of 20 g of dodecane and 20 g of hexadecane. After stirring evenly, the mixture was transferred to a hydrothermal reactor and stirred at 200 °C for 24 h. After filtration, washing, and drying, the mixture was mixed with 10 g of urea and ball-milled at 500 r / min for 3 h in a planetary ball mill. Subsequently, the mixture was calcined at 400 °C for 4 h under nitrogen atmosphere to obtain nitrogen-doped hydrophobic graphite support.

[0049] S2: Loaded with insoluble Mg and Fe species Weigh 16.11 g of ferric nitrate nonahydrate and 6.83 g of magnesium nitrate hexahydrate, dissolve them in deionized water, and prepare Fe... 3+ and Mg 2+ A 1.0 mol / L metal salt solution was prepared. Sodium carbonate was dissolved in deionized water to prepare a 1.0 mol / L sodium carbonate solution. 3.23 g of nitrogen-doped hydrophobic graphite support was mixed with 100 mL of deionized water to form a suspension. The metal salt solution and sodium carbonate solution were added dropwise in parallel to the suspension to induce a precipitation reaction. During the precipitation reaction, the pH was controlled to 9 by controlling the dropwise addition rates of solutions A and B, and the temperature was controlled at 70℃. The precipitation reaction time was 30 min. After the precipitation reaction was completed, the solution was allowed to stand for 2 h, filtered 5 times, dried at 100℃, and ground to obtain the catalyst precursor powder.

[0050] S3: Loaded with alkali metal elements Take 1 g of catalyst precursor powder and add it to 5 mL of sodium nitrate aqueous solution with a concentration of 0.0076 g / mL. After sonication for 2 h, dry at 120℃ to obtain modified precursor powder.

[0051] S4: Load Ag + and Ag 0 Weigh 0.005 g of silver nitrate and dissolve it in deionized water to prepare a silver nitrate solution with a concentration of 0.001 g / mL. Weigh 0.01 g of NaBH4 and dissolve it in deionized water to prepare a NaBH4 solution with a concentration of 0.001 g / mL. Mix all the modified precursor powder obtained in step S3 with 20 mL of deionized water. At 10 °C, add silver nitrate solution dropwise at a rate of 1 mL / min. After the addition is complete, continue stirring for 30 min to allow adsorption equilibrium to be reached. Then, add 1 mL of NaBH4 solution and stir for 10 min. Dry at 40 °C to obtain the silver-loaded precursor powder.

[0052] S5: Calcination and Post-processing The silver-loaded precursor powder was calcined at 500℃ for 6 h under nitrogen atmosphere, cooled, pressed into tablets at 10 MPa, crushed, and sieved to obtain 40-60 mesh particles, thus obtaining the Mg-Fe-Ag composite hydrogenation catalyst.

[0053] Example 3: Preparation of Mg-Fe-Ag composite hydrogenation catalyst This embodiment prepares the Mg-Fe-Ag composite hydrogenation catalyst according to the following steps: S1: Preparation of nitrogen-doped hydrophobic graphite carriers 20 g of graphite powder was dispersed in a mixture of 20 g of dodecane and 20 g of hexadecane. After stirring evenly, the mixture was transferred to a hydrothermal reactor and stirred at 300 °C for 4 h. After filtration, washing, and drying, the mixture was mixed with 10 g of urea and ball-milled at 700 r / min for 250 min in a planetary ball mill. Subsequently, the mixture was calcined at 600 °C for 4 h under nitrogen atmosphere to obtain nitrogen-doped hydrophobic graphite support.

[0054] S2: Loaded with insoluble Mg and Fe species Weigh 16.11 g of ferric nitrate nonahydrate and 4.10 g of magnesium nitrate hexahydrate, dissolve them in deionized water, and prepare Fe... 3+ and Mg 2+ A 1.0 mol / L metal salt solution was prepared. Sodium carbonate was dissolved in deionized water to prepare a 1.0 mol / L sodium carbonate solution. 9.696 g of nitrogen-doped hydrophobic graphite support was mixed with 100 mL of deionized water to form a suspension. The metal salt solution and sodium carbonate solution were added dropwise in a parallel stream to induce a precipitation reaction. During the precipitation, the pH was controlled to 10 by adjusting the dropwise rates of solutions A and B, and the temperature was maintained at 80℃ for 30 min. After the precipitation reaction was complete, the mixture was allowed to stand for 2 h, filtered five times, dried at 110℃, and ground to obtain the catalyst precursor powder.

[0055] S3: Loaded with alkali metal elements Take 1 g of catalyst precursor powder and add it to 5 mL of sodium nitrate aqueous solution with a concentration of 0.0126 g / mL. After sonication for 2 h, dry at 140℃ to obtain modified precursor powder.

[0056] S4: Load Ag + and Ag 0 Weigh 0.015 g of silver nitrate and dissolve it in deionized water to prepare a silver nitrate solution with a concentration of 0.001 g / mL. Weigh 0.01 g of NaBH4 and dissolve it in deionized water to prepare a NaBH4 solution with a concentration of 0.001 g / mL. Mix all the modified precursor powder obtained in step S3 with 30 mL of deionized water. At 10 °C, add silver nitrate solution dropwise at a rate of 1 mL / min. After the addition is complete, continue stirring for 30 min to allow adsorption equilibrium to be reached. Then, add 1 mL of NaBH4 solution and stir for 10 min. Dry at 40 °C to obtain the silver-loaded precursor powder.

[0057] S5: Calcination and Post-processing The silver-loaded precursor powder was calcined at 600℃ for 2 h under nitrogen atmosphere, cooled, pressed into tablets at 10 MPa, crushed, and sieved to obtain 40-60 mesh particles, thus obtaining the Mg-Fe-Ag composite hydrogenation catalyst.

[0058] Comparative Example 1: Preparation of Mg-Fe composite hydrogenation catalyst The only difference between this comparative example and Example 1 is that it is unloaded with Ag. + and Ag 0 That is, step S4 was not performed; the remaining raw materials and steps were the same as in Example 1. Specifically, this comparative example prepared a Mg-Fe composite hydrogenation catalyst according to the following steps: S1: Preparation of nitrogen-doped hydrophobic graphite carriers 20 g of graphite powder was dispersed in a mixture of 20 g of dodecane and 20 g of hexadecane. After stirring evenly, the mixture was transferred to a hydrothermal reactor and stirred at 220 °C for 8 h. After filtration, washing, and drying, the mixture was mixed with 10 g of urea and ball-milled at 400 r / min for 3 h in a planetary ball mill. Subsequently, the mixture was calcined at 500 °C for 4 h under nitrogen atmosphere to obtain nitrogen-doped hydrophobic graphite support.

[0059] S2: Loaded with insoluble Mg and Fe species Weigh 16.11 g of ferric nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate, dissolve them in deionized water, and prepare Fe... 3+ and Mg 2+A 1.0 mol / L metal salt solution was prepared. Sodium carbonate was dissolved in deionized water to prepare a 1.0 mol / L sodium carbonate solution. 6.464 g of nitrogen-doped hydrophobic graphite support was mixed with 100 mL of deionized water to form a suspension. The metal salt solution and sodium carbonate solution were added dropwise in a parallel stream to induce a precipitation reaction. During the precipitation, the pH was controlled to 8 by adjusting the dropwise rates of solutions A and B, and the temperature was maintained at 60℃ for 30 min. After the precipitation reaction was complete, the mixture was allowed to stand for 2 h, filtered five times, dried at 120℃, and ground to obtain the catalyst precursor powder.

[0060] S3: Loaded with alkali metal elements Take 1 g of catalyst precursor powder and add it to 5 mL of sodium carbonate aqueous solution with a concentration of 0.0092 g / mL. After sonication for 2 h, dry at 120℃ to obtain modified precursor powder.

[0061] S4: Calcination and Post-processing The modified precursor powder was calcined at 550℃ for 4 h under nitrogen atmosphere, cooled, pressed into tablets at 10 MPa, crushed, and sieved to obtain 40-60 mesh particles, thus obtaining the Mg-Fe composite hydrogenation catalyst.

[0062] Comparative Example 2: Preparation of Mg-Fe-Ag Composite Hydrogenation Catalyst The only difference between this comparative example and Example 1 is that in step S4, the amount of reducing agent was increased and the reduction reaction time was extended; the remaining raw materials and steps are the same as in Example 1. Specifically, this comparative example prepares the Mg-Fe-Ag composite hydrogenation catalyst according to the following steps: S1: Preparation of nitrogen-doped hydrophobic graphite carriers 20 g of graphite powder was dispersed in a mixture of 20 g of dodecane and 20 g of hexadecane. After stirring evenly, the mixture was transferred to a hydrothermal reactor and stirred at 220 °C for 8 h. After filtration, washing, and drying, the mixture was mixed with 10 g of urea and ball-milled at 400 r / min for 3 h in a planetary ball mill. Subsequently, the mixture was calcined at 500 °C for 4 h under nitrogen atmosphere to obtain nitrogen-doped hydrophobic graphite support.

[0063] S2: Loaded with insoluble Mg and Fe species Weigh 16.11 g of ferric nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate, dissolve them in deionized water, and prepare Fe... 3+ and Mg 2+A 1.0 mol / L metal salt solution was prepared. Sodium carbonate was dissolved in deionized water to prepare a 1.0 mol / L sodium carbonate solution. 6.464 g of nitrogen-doped hydrophobic graphite support was mixed with 100 mL of deionized water to form a suspension. The metal salt solution and sodium carbonate solution were added dropwise in a parallel stream to induce a precipitation reaction. During the precipitation, the pH was controlled to 8 by adjusting the dropwise rates of solutions A and B, and the temperature was maintained at 60℃ for 30 min. After the precipitation reaction was complete, the mixture was allowed to stand for 2 h, filtered five times, dried at 120℃, and ground to obtain the catalyst precursor powder.

[0064] S3: Loaded with alkali metal elements Take 1 g of catalyst precursor powder and add it to 5 mL of sodium carbonate aqueous solution with a concentration of 0.0092 g / mL. After sonication for 2 h, dry at 120℃ to obtain modified precursor powder.

[0065] S4: Load Ag + and Ag 0 Weigh 0.01 g of silver nitrate and dissolve it in deionized water to prepare a silver nitrate solution with a concentration of 0.001 g / mL. Weigh 0.01 g of NaBH4 and dissolve it in deionized water to prepare a NaBH4 solution with a concentration of 0.001 g / mL. Mix all the modified precursor powder obtained in step S3 with 30 mL of deionized water. At 10 °C, add silver nitrate solution dropwise at a rate of 1 mL / min. After the addition is complete, continue stirring for 30 min to allow adsorption equilibrium to be reached. Then, add 10 mL of NaBH4 solution and stir for 20 min. Dry at 40 °C to obtain the silver-loaded precursor powder.

[0066] S5: Calcination and Post-processing The silver-loaded precursor powder was calcined at 550℃ for 4 h under nitrogen atmosphere, cooled, pressed into tablets at 10 MPa, crushed, and sieved to obtain 40-60 mesh particles, thus obtaining the Mg-Fe-Ag composite hydrogenation catalyst.

[0067] Comparative Example 3: Preparation of Mg-Fe-Ag Composite Hydrogenation Catalyst The only difference between this comparative example and Example 1 is that, in step S4, no reducing agent was added to Ag. + The reduction reaction was carried out; the remaining raw materials and steps were the same as in Example 1. Specifically, this comparative example prepared the Mg-Fe-Ag composite hydrogenation catalyst according to the following steps: S1: Preparation of nitrogen-doped hydrophobic graphite carriers 20 g of graphite powder was dispersed in a mixture of 20 g of dodecane and 20 g of hexadecane. After stirring evenly, the mixture was transferred to a hydrothermal reactor and stirred at 220 °C for 8 h. After filtration, washing, and drying, the mixture was mixed with 10 g of urea and ball-milled at 400 r / min for 3 h in a planetary ball mill. Subsequently, the mixture was calcined at 500 °C for 4 h under nitrogen atmosphere to obtain nitrogen-doped hydrophobic graphite support.

[0068] S2: Loaded with insoluble Mg and Fe species Weigh 16.11 g of ferric nitrate nonahydrate and 5.12 g of magnesium nitrate hexahydrate, dissolve them in deionized water, and prepare Fe... 3+ and Mg 2+ A 1.0 mol / L metal salt solution was prepared. Sodium carbonate was dissolved in deionized water to prepare a 1.0 mol / L sodium carbonate solution. 6.464 g of nitrogen-doped hydrophobic graphite support was mixed with 100 mL of deionized water to form a suspension. The metal salt solution and sodium carbonate solution were added dropwise in a parallel stream to induce a precipitation reaction. During the precipitation, the pH was controlled to 8 by adjusting the dropwise rates of solutions A and B, and the temperature was maintained at 60℃ for 30 min. After the precipitation reaction was complete, the mixture was allowed to stand for 2 h, filtered five times, dried at 120℃, and ground to obtain the catalyst precursor powder.

[0069] S3: Loaded with alkali metal elements Take 1 g of catalyst precursor powder and add it to 5 mL of sodium carbonate aqueous solution with a concentration of 0.0092 g / mL. After sonication for 2 h, dry at 120℃ to obtain modified precursor powder.

[0070] S4: Load Ag + Weigh 0.01 g of silver nitrate and dissolve it in deionized water to prepare a silver nitrate solution with a concentration of 0.001 g / mL. Mix all the modified precursor powder obtained in step S3 with 30 mL of deionized water. Add the silver nitrate solution dropwise at a rate of 1 mL / min at 10°C. After the addition is complete, continue stirring for 30 min to allow adsorption equilibrium to be reached. Dry the mixture at 40°C to obtain the silver-loaded precursor powder.

[0071] S5: Calcination and Post-processing The silver-loaded precursor powder was calcined at 550℃ for 4 h under nitrogen atmosphere, cooled, pressed into tablets at 10 MPa, crushed, and sieved to obtain 40-60 mesh particles, thus obtaining the Mg-Fe-Ag composite hydrogenation catalyst.

[0072] Test Example 1: CO2 Conversion Rate and Product Selectivity Test Catalysts prepared according to the methods in Examples 1-3 and Comparative Examples 1-2 (at least 5 valid data points were taken for each example and comparative example, and the average value of the test results were used) were used to catalyze the CO2 hydrogenation to olefins reaction to test the CO2 conversion rate and product selectivity. The specific process is as follows: Before the CO2 hydrogenation to olefins reaction, 0.25 g of catalyst was loaded into a fixed-bed reactor. After checking the airtightness, the temperature was raised to 350°C at 5°C / min, and hydrogen gas was introduced at a flow rate of 25 mL / min for 5 h for reduction. Then, it was naturally cooled in the hydrogen gas flow. During the reaction, a mixed gas with a H2 / CO2 volume ratio of 3:1 was introduced at a flow rate of 30 mL / min, and the temperature was raised to 300°C at a rate of 5°C / min. After the reaction, the heating was stopped first, and the mixed gas was introduced to cool down. Finally, the valve was closed, the device was disassembled, and the product and catalyst were disposed of. The product was analyzed by gas chromatography, and the CO2 conversion rate, total olefin selectivity, and methane selectivity were calculated. The results are shown in Table 1. Among them, the composition of alkanes and olefins in the product when using the catalyst of Example 1 is shown in Table 1. Figure 1 .

[0073] Table 1. Results of CO2 conversion rate and product selectivity tests

[0074] The test results in Table 1 show that: (1) Compared with Comparative Example 1, the CO2 conversion and total olefin selectivity of Example 1 were significantly improved, and the difference was statistically significant (p<0.05). Methane selectivity decreased. This is because, based on Comparative Example 1, Example 1 introduced Ag at a specific position on the catalyst. + and Ag 0 Among them, Ag doped into iron oxide + It can distort its crystal lattice, generating oxygen vacancies and surface defects, becoming active centers for catalytic reactions and improving the reaction efficiency of CO2 hydrogenation to olefins; Ag distributed on the surface of Mg-Fe modified graphite + It can suppress methanation side reaction sites during CO2 hydrogenation, thereby reducing the formation of methane byproduct and improving olefin selectivity; Ag supported between Mg-Fe modified graphite layers 0 It can serve as a CO adsorption and activation site, further improving reaction efficiency; and Ag + and Ag 0 This differentiated spatial distribution can also promote in-plane and interlayer charge transport, thus facilitating catalytic reactions.

[0075] (2) Compared with Comparative Example 2, Example 1 showed higher total olefin selectivity and lower methane selectivity, with a significant difference (p<0.05). This is because: in the catalyst of Example 1, the surface-supported Ag... +It can suppress methanation side reaction sites during CO2 hydrogenation and improve olefin selectivity; Comparative Example 2, when loaded with Ag species, is reduced to Ag. 0 Ag + Excessive amounts of Ag will cause problems with the distribution of Ag on the catalyst surface. + Relatively few.

[0076] (3) Compared with Comparative Example 3, the CO2 conversion rate of Example 1 was higher, and the difference was significant (p<0.05). This is because: in the catalyst of Example 1, the Ag supported between layers... 0 It can serve as a CO adsorption and activation site, improving reaction efficiency; in Comparative Example 3, when Ag species were loaded, no reducing agent was added to reduce Ag... + Partially reduced to Ag 0 It is impossible to load a large amount of Ag onto the interlayer of the catalyst. 0 .

[0077] Test Example 2: Catalyst Stability Test The catalysts prepared according to the methods in Examples 1-3 and Comparative Example 1 were used to catalyze the CO2 hydrogenation to olefins reaction, and the stability of the catalysts was tested. The specific process is as follows: Before the CO2 hydrogenation to olefins reaction, 0.25 g of catalyst was loaded into a fixed-bed reactor. After checking the airtightness, the temperature was raised to 350°C at 5°C / min, and hydrogen was introduced at a flow rate of 25 mL / min for 5 h for reduction. Then, the reactor was naturally cooled in a hydrogen flow. During the reaction, a mixed gas with a volume ratio of H2 / CO2 of 3:1 was introduced at a flow rate of 30 mL / min, and the temperature was raised to 300°C at a rate of 5°C / min. The reaction was continued for 1000 h. During this period, the product was analyzed by gas chromatography every 30 min, and the CO2 conversion rate was calculated. After the reaction was completed, the heating was stopped, the mixed gas was introduced to cool down, and finally the valve was closed, the device was disassembled, and the product and catalyst were disposed of.

[0078] Stability test results showed that, using the catalysts of Examples 1-3 and Comparative Example 1, the CO2 conversion rate did not decrease significantly during continuous operation for 1000 h (wherein, the test results of Example 1 are as follows). Figure 2 As shown), this indicates that Ag in this invention + and Ag 0 The introduction of Mg will not affect the effect of Mg in improving the stability of iron-based catalysts.

[0079] Test Example 3: Analysis of the Valence State of Ag Atom The catalyst from Example 1, after completing the stability test in Test Example 2, was subjected to X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis. The obtained spectra are shown below. Figure 3 and Figure 5As shown; after etching the catalyst with argon ions for 1 min, XPS analysis was performed again, and the obtained spectrum is shown below. Figure 4 As shown. XRD analysis results indicate that the sample contains Ag element ( Figure 5 XPS analysis results showed that the Ag element on the sample surface before etching was mainly Ag. + The form of existence ( Figure 3 Ag was present on the surface of the etched sample. 0 ( Figure 4 This indicates that the catalyst of the present invention, when used in the catalytic hydrogenation of CO2 to olefins, can maintain its "surface distribution of Ag". + Ag is distributed in the interlayer. 0 The structure is "".

Claims

1. A Mg-Fe-Ag composite hydrogenation catalyst, characterized in that, The invention includes Mg-Fe modified graphite; the Mg-Fe modified graphite comprises a graphite support, and iron oxide and magnesium oxide supported on the graphite support; the iron oxide is doped with Ag. + The Mg-Fe modified graphite has Ag loaded on its surface. + And the interlayer load has Ag 0 .

2. The Mg-Fe-Ag composite hydrogenation catalyst according to claim 1, characterized in that, The graphite carrier is a hydrophobic graphite carrier doped with nitrogen atoms.

3. The Mg-Fe-Ag composite hydrogenation catalyst according to claim 1 or 2, characterized in that, The graphite carrier also contains alkali metal elements.

4. A method for preparing the Mg-Fe-Ag composite hydrogenation catalyst according to any one of claims 1 to 3, characterized in that, step include: S1: Containing Mg 2+ and Fe 3+ The solution and the precipitant solution were added dropwise to the graphite carrier dispersion to carry out a precipitation reaction, and the product was separated. S2: Disperse the product of S1 in water, add Ag-containing... + After the solution reaches adsorption equilibrium, a reducing agent is added to initiate a reduction reaction, causing some Ag to be released. + Convert to Ag 0 Dry and calcine.

5. The preparation method according to claim 4, characterized in that, In step S2: The reducing agent is NaBH4, Ag + The mass ratio of NaBH4 to NaBH4 is 1:0.1~1, the reduction reaction temperature is 20~25℃, and the time is 10~15 min; or, The reducing agent is ascorbic acid, Ag. + The mass ratio of ascorbic acid to ascorbic acid is 1:1~2, the temperature of the reduction reaction is 20~60℃, and the time is 1~4 h.

6. The preparation method according to claim 4, characterized in that, In step S1, the Mg 2+ with Fe 3+ The molar ratio of the graphite carrier and Fe is 1:1.5~2.

5. 3+ The mass ratio is 1:0.2~0.7; in step S2, the Ag... + The dosage is 0.5~1.5 wt% of the S1 product, wherein the Ag-containing product... + Ag in solution + The content is 0.001~0.005 g / mL, with the addition of Ag. + The solution flow rate is 1-3 mL / min, and the adsorption equilibrium time is 20-40 min.

7. The preparation method according to claim 4, characterized in that, Before step S1, the graphite support is hydrophobically modified and doped with nitrogen atoms. The specific process includes: dispersing the graphite support in a mixture of dodecane and hexadecane, stirring it evenly, stirring it at 200~300℃ for 4~24 h, separating the product, mixing it with urea and ball milling it, and calcining it at 400~600℃ for 3.5~4.5 h in an inert atmosphere.

8. The preparation method according to claim 4, characterized in that, Before step S2, alkali metal elements are loaded onto the product of S1. The specific process includes: adding the product of S1 into a solution containing alkali metal ions, ultrasonically treating it, and then drying it.

9. The application of the Mg-Fe-Ag composite hydrogenation catalyst according to any one of claims 1 to 3 in the catalytic hydrogenation of CO2 to olefins.

10. The application according to claim 9, characterized in that, During the CO2 hydrogenation to olefins reaction, the temperature is 300~350℃, the volume ratio of H2 to CO2 is 2.5~3.5:1, and the flow rate of the H2 and CO2 mixture is 20~30 mL / min.

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