Ni / sod-based alkali metal molecular sieve catalyst as well as synthesis method and application thereof

Abstract

The invention discloses a Ni / sod-based alkali metal molecular sieve catalyst and a synthesis method and application thereof, and relates to the technical field of catalysts, the synthesis method comprises the following steps: mixing fly ash with an alkali source, and carrying out microwave-alkali treatment to obtain a solid treatment substance; mixing the solid treatment substance with water, and carrying out crystallization treatment to obtain the sod molecular sieve; the method comprises the following steps: mixing the sod molecular sieve with a nickel salt solution, carrying out dipping treatment, dissolving, recrystallizing, roasting and carrying out hydrogen reduction to obtain the Ni / sod-based alkali metal molecular sieve catalyst. The Ni / sod-based alkali metal molecular sieve catalyst has good thermal stability, adsorption performance and catalytic activity, can effectively catalyze methanation of carbon dioxide, and has important economic and environmental significance.

Description

Technical Field

[0001] The present invention relates to a Ni / sod-based alkali metal molecular sieve catalyst, a synthesis method thereof, and an application thereof, belonging to the technical field of catalysts. Background Art

[0002] Fly ash is an industrial solid waste discharged from coal-fired power plants. Its main components are silica and alumina, and it has a relatively high silicon-aluminum ratio. Traditional fly ash treatment methods are mostly landfill or stacking, which not only occupy a large amount of land resources but also may cause environmental pollution. Therefore, how to effectively utilize the silicon-aluminum resources in fly ash and convert them into high-value-added materials has important research significance.

[0003] Carbon dioxide (CO2) is a greenhouse gas, and its emission has an important impact on global climate change. Converting CO2 into methane (CH4) can realize the resource utilization of carbon dioxide and is an important link in the carbon cycle. In the reaction of CO2 hydrogenation to CH4, due to the high stability and inertness of CO2, the reaction temperature is high, while the CO2 conversion rate is relatively low, and by-products such as carbon monoxide and methanol will be produced. Therefore, the performance of the catalyst is crucial.

[0004] In the field of carbon dioxide methanation catalysts, transition metal catalysts have received much attention. Compared with molecular catalysts with limited loading and complex coordination environments, and noble metal catalysts with high costs, transition metal catalysts have advantages such as high activity and good selectivity. Among them, as a member of transition metal catalysts, nickel-based catalysts are very promising in the field of carbon dioxide methanation due to their high activity and low cost, and have become the research focus in this field.

[0005] Regarding nickel-based catalysts, researchers have explored various carriers and preparation methods. For example, when preparing a nickel-based catalyst with alumina as the carrier by the impregnation method, although the activity is good in the initial stage, problems gradually appear as the reaction proceeds. During the high-temperature reaction process, the nickel active component is prone to sintering. This sintering reduces the number of active sites, resulting in a decrease in catalytic activity. In addition, carbon deposition will also occur on the catalyst surface. The carbon deposition not only blocks the active sites but also affects the selectivity of the catalyst, ultimately leading to a decrease in the conversion rate of carbon dioxide to methane.

[0006] Similarly, for a nickel-based catalyst with silica as the carrier prepared by the sol-gel method, although the nickel particles are expected to be evenly distributed in the initial stage, this catalyst still has stability problems. Under specific reaction conditions, metallic nickel is easily oxidized, and the subsequent reduction process will cause the nickel particles to agglomerate. This agglomeration phenomenon not only increases the complexity of the preparation process because precise reaction conditions need to be controlled to avoid it, but also significantly reduces the stability of the catalyst, making it more likely to deactivate during long-term use.

[0007] Problems such as metal sintering, carbon deposition, and aggregation of active components in nickel-based catalysts not only lead to poor stability but also increase the complexity of the preparation process. These problems directly restrict the wide application of nickel-based catalysts in the carbon dioxide methanation reaction, highlighting the urgent need to solve these technical problems. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a Ni / sod-based alkali metal molecular sieve catalyst, its synthesis method, and application. It has good thermal stability, adsorption performance, and catalytic activity, can effectively catalyze carbon dioxide methanation, and has important economic and environmental significance.

[0009] To achieve the above purpose, the present invention is implemented by the following technical solutions: In the first aspect, the present invention provides a synthesis method of a Ni / sod-based alkali metal molecular sieve catalyst, including: Mix fly ash with an alkali source and perform microwave-alkali treatment to obtain a solid treatment product; Place the solid treatment product in water for crystallization treatment to obtain sod-type molecular sieves; Immerse the sod-type molecular sieves in a nickel salt solution to obtain impregnated sod-type molecular sieves; Dissolve and recrystallize the impregnated sod-type molecular sieves, and then perform calcination and hydrogen reduction to obtain a Ni / sod-based alkali metal molecular sieve catalyst.

[0010] Further, the alkali source is at least one of alkali metal hydroxides and alkaline earth metal hydroxides; and / or, the mass ratio of fly ash to the alkali source is 1:0.5 - 50.

[0011] Further, the framework type of the sod-type molecular sieves is one of LTA, FAU, SOD, LTN, EMT, FAR, GIU, MAR, TSC, and FRA.

[0012] Further, the nickel salt solution is at least one of nickel nitrate and nickel chloride; the concentration range of the nickel salt solution is 0.1 - 0.5 mol / L.

[0013] Further, both the dissolution and recrystallization are carried out in a tetrapropylammonium hydroxide solution, and the concentration range of the tetrapropylammonium hydroxide solution is 0.3 - 0.8 mol / L.

[0014] Further, the temperature range for dissolution is 50 - 100 °C; and / or, the condition parameters for recrystallization include a temperature range of 100 - 200 °C and a time range of 12 - 24 h.

[0015] Further, the condition parameters of the microwave-alkali treatment include treating with a microwave power of 500-1000 W for 10-20 min; And / or, the condition parameters of the crystallization treatment include treating in a temperature range of 90-200 °C for 24-72 h; And / or, the condition parameters of the impregnation treatment include treating at room temperature for 12-24 h; And / or, the condition parameters of the calcination include treating at 500-700 °C for 4-12 h; And / or, the condition parameters of the hydrogen reduction include a temperature range of 500-700 °C, a reaction pressure of 1-5 MPa, and a gas flow rate of 50-100 mL / min.

[0016] In a second aspect, the present invention also provides a Ni / sod-based alkali metal molecular sieve catalyst, which is synthesized by the synthesis method of the Ni / sod-based alkali metal molecular sieve catalyst as described in any one of the above.

[0017] In a third aspect, the present invention also provides an application of the above Ni / sod-based alkali metal molecular sieve catalyst, including as a catalyst in the carbon dioxide methanation reaction.

[0018] Further, the condition parameters of the carbon dioxide methanation reaction include in a temperature range of 300-700 °C, a reaction pressure of 2-10 MPa, a gas flow rate of 10-200 mL / min, and a volume ratio of carbon dioxide to hydrogen of 1:1-10.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention: The present invention uses microwave-alkali treatment for activation, reducing the activation energy consumption of raw materials. After impregnation treatment, dissolution and recrystallization treatment can make the substance to be impregnated dissolve fully in the solvent, making the solute more evenly distributed on the surface and in the pores of the sod-type molecular sieve. Hydrogen reduction can not only reduce Ni to the active state but also remove impurities, adjust the Ni particle size, and improve the activity and selectivity of the Ni / sod-based alkali metal molecular sieve catalyst; The Ni / sod-based alkali metal molecular sieve catalyst prepared by the present invention has good thermal stability, adsorption and catalytic activity, can effectively catalyze the carbon dioxide methanation reaction, and has important economic and environmental significance. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of the Ni-based LTA-type molecular sieve catalyst synthesized in Example 1 of the present invention; Figure 2 It is an X-ray diffraction schematic diagram of the Ni-based FAU-type molecular sieve catalyst synthesized in Example 2 of the present invention; Figure 3 Scanning electron microscope schematic diagram of the Ni-based FAU zeolite catalyst synthesized in Example 2 of the present invention; Figure 4 X-ray diffraction schematic diagram of the commercial FAU zeolite catalyst of Comparative Example 1 of the present invention; Figure 5 X-ray diffraction comparison schematic diagram between the Ni-based FAU zeolite catalyst synthesized in Example 2 of the present invention and the commercial FAU zeolite catalyst of Comparative Example 1. Detailed implementation manners

[0021] The present invention will be further described below with reference to the accompanying drawings. The following examples are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0022] Example 1

[0023] The present invention provides a method for synthesizing a Ni-based LTA zeolite catalyst, which includes the following steps: S1. Mix 10 g of fly ash and 5 g of sodium hydroxide, and then treat them in a microwave synthesizer at a microwave power of 700 W for 15 minutes at room temperature. Filter and dry the product to obtain a solid treatment product.

[0024] S2. Mix the solid treatment product with water, transfer it to a hydrothermal synthesis reaction kettle with a polytetrafluoroethylene inner liner, and crystallize it at 90 °C for 48 hours to obtain an LTA zeolite.

[0025] S3. Mix the LTA zeolite with a 0.1 mol / L nickel nitrate solution and impregnate it at room temperature for 24 hours to obtain an impregnated zeolite.

[0026] S4. Dissolve the impregnated zeolite in a 0.5 mol / L tetrapropylammonium hydroxide (TPAOH) solution at 60 °C for 2 hours, and then recrystallize it at 120 °C for 12 hours to obtain a recrystallized zeolite.

[0027] S5. Put the recrystallized zeolite into a muffle furnace and calcine it at 550 °C for 6 hours to obtain a calcined zeolite.

[0028] S6. Cool the calcined zeolite to room temperature and then put it into a tubular furnace. Carry out hydrogen reduction at 600 °C and 3 MPa, with a gas flow rate of 80 mL / min and a reduction time of 2 hours to obtain a Ni-based LTA zeolite catalyst. The structure of the Ni-based LTA zeolite catalyst is as Figure 1 shown, where the yellow framework is the topological structure of the LTA zeolite, and the silver spheres located inside the topological structure are nickel.

[0029] Example 2

[0030] An embodiment of the present invention provides a method for synthesizing a Ni-based FAU zeolite catalyst, comprising the following steps: S1. After mixing 10 g of fly ash and 10 g of potassium hydroxide, treat the mixture in a microwave synthesizer at a microwave power of 700 W for 15 minutes at room temperature. Add 12 g of sodium silicate to the solution (silicon source needs to be supplemented to adjust the silicon-aluminum ratio for synthesizing FAU zeolite), continue microwave treatment for 10 minutes, filter and dry the product to obtain a solid treated product.

[0031] S2. Mix the solid treated product with water, transfer it to a hydrothermal synthesis reactor with a polytetrafluoroethylene inner liner, and crystallize at 100 °C for 24 hours to obtain FAU zeolite.

[0032] S3. Mix the FAU zeolite with a 0.5 mol / L nickel chloride solution, and impregnate at room temperature for 24 hours to obtain an impregnated zeolite.

[0033] S4. Dissolve the impregnated zeolite in a 0.8 mol / L TPAOH solution at 70 °C for 3 hours, and then recrystallize at 150 °C for 18 hours to obtain a recrystallized zeolite.

[0034] S5. Put the recrystallized zeolite into a muffle furnace and calcine at 600 °C for 8 hours to obtain a calcined zeolite.

[0035] S6. Cool the calcined zeolite to room temperature and put it into a tubular furnace. Carry out hydrogen reduction at 600 °C and 3 MPa, with a gas flow rate of 90 mL / min, and reduce for 3 hours to obtain a Ni-based FAU zeolite catalyst.

[0036] The X-ray diffraction pattern of the Ni-based FAU zeolite catalyst is as Figure 2 shown. It can be seen from the figure that the crystal structure of the Ni-based FAU zeolite catalyst is good.

[0037] The scanning electron microscope image of the Ni-based FAU zeolite catalyst is as Figure 3 shown. In the figure, the crystal shape of the Ni-based FAU zeolite catalyst is regular and the particles are evenly dispersed.

[0038] Example 3

[0039] This embodiment provides a method for synthesizing a Ni-based SOD zeolite catalyst, comprising the following steps: S1. After mixing 10 g of fly ash and 8 g of sodium hydroxide, treat the mixture in a microwave synthesizer at a microwave power of 700 W for 15 minutes at room temperature, filter and dry the product to obtain a solid treated product.

[0040] S2. Mix the solid treatment product with water, transfer it to a hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and crystallize it at 95 °C for 36 hours to obtain SOD-type molecular sieve.

[0041] S3. Mix the SOD-type molecular sieve with a mixed solution of 0.3 mol / L nickel nitrate and nickel chloride (volume ratio 1:1), and impregnate it at room temperature for 18 hours to obtain the impregnated molecular sieve.

[0042] S4. Dissolve the impregnated molecular sieve in 0.3 mol / L TPAOH solution at 65 °C for 2.5 hours, and then recrystallize it at 130 °C for 20 hours to obtain the recrystallized molecular sieve.

[0043] S5. Put the recrystallized molecular sieve into a muffle furnace and calcine it at 650 °C for 10 hours to obtain the calcined molecular sieve.

[0044] S6. Cool the calcined molecular sieve to room temperature and then put it into a tubular furnace. Reduce it with hydrogen at 600 °C and 3 MPa, with a gas flow rate of 100 mL / min for 3 hours to obtain the Ni-based SOD-type molecular sieve catalyst.

[0045] Example 4

[0046] This example provides a method for synthesizing a Ni-based LTN-type molecular sieve catalyst, which includes the following steps: S1. Mix 10 g of fly ash, 12 g of sodium hydroxide and 3 g of potassium hydroxide, and treat them in a microwave synthesizer at a microwave power of 700 W at room temperature for 15 minutes. Filter and dry the product to obtain the solid treatment product.

[0047] S2. Mix the solid treatment product with water, transfer it to a hydrothermal synthesis reactor with a polytetrafluoroethylene liner, and crystallize it at 90 °C for 42 hours to obtain LTN-type molecular sieve.

[0048] S3. Mix the LTN-type molecular sieve with 0.2 mol / L nickel nitrate solution, and impregnate it at room temperature for 20 hours to obtain the impregnated molecular sieve.

[0049] S4. Dissolve the impregnated molecular sieve in 0.4 mol / L TPAOH solution at 60 °C for 1.5 hours, and then recrystallize it at 110 °C for 16 hours to obtain the recrystallized molecular sieve.

[0050] S5. Put the recrystallized molecular sieve into a muffle furnace and calcine it at 580 °C for 7 hours to obtain the calcined molecular sieve.

[0051] S6. After cooling the calcined molecular sieve to room temperature, place it in a tubular furnace and carry out hydrogen reduction at 600 °C and 3 MPa. The gas flow rate is 70 mL / min, and the reduction is carried out for 2.5 hours to obtain a Ni-based LTN-type molecular sieve catalyst.

[0052] The differences in the synthesis methods of the above Examples 1 to 4 are specifically shown in Table 1.

[0053] Table 1: Synthesis conditions of Examples 1 to 4

[0054] Comparative Example 1: This comparative example provides a commercial FAU-type molecular sieve catalyst. The difference in its synthesis method from that of Example 2 is only that the impregnation loading and dissolution-recrystallization treatment are not carried out.

[0055] The X-ray diffraction pattern of the commercial FAU-type molecular sieve catalyst is as Figure 4 shown. The crystal structure of the FAU-type molecular sieve catalyst is good, which effectively proves the effective preparation of the FAU-type molecular sieve catalyst.

[0056] Comparative Example 2: This comparative example provides a synthesis method of a Ni-based FAU-type molecular sieve catalyst. The difference from that of Example 2 is only that the dissolution-recrystallization treatment is not carried out after the impregnation treatment.

[0057] Next, the molecular sieve catalysts synthesized in Examples 1 to 4 and Comparative Examples 1 to 2 are subjected to performance analysis.

[0058] First, the X-ray diffraction patterns of the Ni-based FAU-type molecular sieve catalyst of Example 2 and the commercial FAU-type molecular sieve catalyst of Comparative Example 1 are compared as Figure 5 shown. It can be seen from the figure that the loading effect of Ni metal in the Ni-based FAU-type molecular sieve catalyst is significant.

[0059] Then, the molecular sieve catalysts synthesized in Examples 1 to 4 and Comparative Examples 1 to 2 are respectively applied to carbon dioxide adsorption. They are degassed under dynamic vacuum at 623 K for 12 hours, backfilled with nitrogen, and cooled to weigh the dry weight.

[0060] The reaction conditions are to introduce a mixed gas of carbon dioxide and nitrogen (volume ratio CO2:N2 = 2:8) at 300 K and 3 bar, the flow rate is 40 mL / min, and the adsorption pressure is 900 kPa. The CO2 adsorption amount of the sample is analyzed by a Micromeritics ASAP 2020 specific surface area analyzer. The results are shown in Table 2.

[0061] Table 2: CO2 adsorption amounts of the molecular sieve catalysts synthesized in Examples 1 to 4 and Comparative Examples 1 to 2

[0062] As can be seen from Table 2, the commercial FAU molecular sieve in Comparative Example 1 has significantly poor adsorption capacity; the carbon dioxide adsorption rate of the Ni / SOD-based alkali metal molecular sieve catalyst in Examples 1 to 4 is significantly improved compared with the FAU-type molecular sieve catalyst that has not been subjected to dissolution-recrystallization treatment in Comparative Example 2, indicating that the dissolution-recrystallization operation can greatly improve the crystal structure of the molecular sieve and enhance the adsorption performance of the Ni / SOD-based alkali metal molecular sieve catalyst. This result proves that the adsorption performance of the Ni / SOD-based alkali metal molecular sieve catalyst after the dissolution-recrystallization operation is significantly improved.

[0063] Finally, the molecular sieve catalysts synthesized in Examples 1 to 4 and Comparative Examples 1 to 2 were respectively applied to carbon dioxide hydrogenation to produce methane. The reaction conditions were: reaction time of 30 min, reaction temperature of 380 ° C, reaction pressure of 300 kPa, volume ratio of carbon dioxide to hydrogen of 1:3, gas flow rate of 40 mL / min per gram of catalyst, and the measured carbon dioxide conversion rate and methane selectivity are shown in Table 3.

[0064] Table 3: Carbon dioxide conversion and methane selectivity of the molecular sieve catalysts synthesized in Examples 1 to 4 and Comparative Examples 1 to 2

[0065] As shown in Table 3, the commercial FAU molecular sieve in Comparative Example 1 has almost no reaction activity to the reaction; the carbon dioxide conversion rate and methane selectivity of the Ni / SOD-based alkali metal molecular sieve catalyst in Examples 1-4 are significantly improved compared with the FAU-type molecular sieve catalyst that has not been subjected to dissolution-recrystallization treatment in Comparative Example 2, indicating that the dissolution-recrystallization operation can greatly improve the catalytic performance of the Ni / SOD-based alkali metal molecular sieve catalyst. This result proves that the performance of the Ni / SOD-based alkali metal molecular sieve catalyst after the dissolution-recrystallization operation in catalyzing the hydrogenation of carbon dioxide to methane is significantly improved.

[0066] In summary, the present invention adopts microwave-alkali treatment instead of traditional high-temperature melting and alkali treatment, which can more efficiently promote the reaction between silicon and aluminum in fly ash and the alkali source and shorten the treatment time.

[0067] The present invention adopts dissolution-recrystallization treatment to enhance the interaction strength between Ni metal load and SOD molecular sieve, and effectively enhances the performance of Ni / SOD-based alkali metal molecular sieve catalyst in catalyzing carbon dioxide hydrogenation to methane reaction.

[0068] The invention uses fly ash as raw material to synthesize Ni / SOD-based alkali metal molecular sieve catalyst, fully utilizes silicon and aluminum resources in the fly ash, reduces raw material costs, and realizes resource utilization of fly ash.

[0069] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for synthesizing a Ni / SOD-based alkali metal molecular sieve catalyst, characterized in that: include: The fly ash is mixed with an alkali source and then subjected to microwave-alkali treatment to obtain a solid treated product; The solid treated product is placed in water for crystallization to obtain a SOD type molecular sieve; The SOD molecular sieve is impregnated in a nickel salt solution to obtain an impregnated SOD molecular sieve; The impregnated SOD molecular sieve is dissolved, recrystallized, calcined and reduced with hydrogen to obtain a Ni / SOD-based alkali metal molecular sieve catalyst.

2. The method for synthesizing a Ni / SOD-based alkali metal molecular sieve catalyst according to claim 1, wherein The alkali source is at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide; and / or the mass ratio of the fly ash to the alkali source is 1:0.5-50.

3. The synthetic method of Ni / SOD based alkali metal molecular sieve catalyst according to claim 1, characterized in that, The framework type of the sod molecular sieve is one of LTA, FAU, SOD, LTN, EMT, FAR, GIU, MAR, TSC and FRA.

4. The method for synthesizing a Ni / SOD-based alkali metal molecular sieve catalyst according to claim 1, wherein The nickel salt solution is at least one of nickel nitrate and nickel chloride; the concentration range of the nickel salt solution is 0.1-0.5 mol / L.

5. The method for synthesizing a Ni / SOD-based alkali metal molecular sieve catalyst according to claim 1, characterized in that: The dissolution and recrystallization are both performed in a tetrapropylammonium hydroxide solution, and the concentration range of the tetrapropylammonium hydroxide solution is 0.3-0.8 mol / L.

6. The method for synthesizing a Ni / SOD-based alkali metal molecular sieve catalyst according to claim 5, characterized in that: The dissolution temperature range is 50-100° C.; and / or the recrystallization condition parameters include a temperature range of 100-200° C. and a time range of 12-24 h.

7. The method for synthesizing a Ni / SOD-based alkali metal molecular sieve catalyst according to claim 1, characterized in that: The microwave-alkali treatment condition parameters include treating with a microwave power of 500-1000 W for 10-20 min; And / or, the crystallization treatment condition parameters include treating at a temperature range of 90-200° C. for 24-72 hours; And / or, the impregnation condition parameters include treating at room temperature for 12 to 24 hours; And / or, the calcination condition parameters include treating at 500-700° C. for 4-12 hours; And / or, the conditions and parameters for hydrogen reduction include a temperature range of 500-700° C., a reaction pressure of 1-5 MPa, and a gas flow rate of 50-100 mL / min.

8. A Ni / SOD-based alkali metal molecular sieve catalyst, characterized in that: The catalyst is synthesized by the synthesis method of the Ni / SOD-based alkali metal molecular sieve catalyst as described in any one of claims 1 to 7.

9. An application of the Ni / SOD-based alkali metal molecular sieve catalyst as claimed in claim 8, characterized in that: Including as a catalyst in the methanation of carbon dioxide.

10. The use of the Ni / sod-based alkali metal molecular sieve catalyst according to claim 9, characterized in that: The condition parameters of the carbon dioxide methanation reaction include a temperature range of 300-700° C., a reaction pressure of 2-10 MPa, a gas flow rate of 10-200 mL / min, and a volume ratio of carbon dioxide to hydrogen of 1:1-10.

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