A rare earth modified mesoporous SiO2 supported nickel catalyst and its preparation method and application

Abstract

The present invention discloses a rare earth metal modified mesoporous silica supported nickel catalyst and its preparation method and application, belonging to the technical field of catalysts. The catalyst of the present invention mainly comprises a rare earth modified mesoporous silica carrier and active metal nickel, wherein the carrier is in situ added with rare earth metal by a template-free sol-gel method to obtain rare earth metal modified mesoporous silica; and the rare earth modified mesoporous silica supported nickel catalyst is obtained after loading metal nickel by an impregnation method. The catalyst of the present invention has very excellent low-temperature carbon dioxide methanation activity and selectivity, can be used to treat carbon dioxide in the atmosphere and industrial waste gas, and convert it into methane, thereby reducing CO2 emissions and recycling.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and particularly relates to a rare earth metal-modified mesoporous silica-supported nickel catalyst and a preparation method and application thereof. Background Art

[0002] Greenhouse gases in the atmosphere, especially CO 2 The increase in concentration leads to global warming and various climate problems. 2 Concentration, mitigating climate warming has become an important challenge that humans must face. In the short term, humans cannot significantly reduce the use of fossil fuels, so CO 2 The large-scale emission of CO will continue for a long time. 2 Conversion into fuels or chemicals is a way to utilize CO 2 , and produce fuels and chemicals, killing two birds with one stone.

[0003] CO 2 The hydrogenation reduction is converted to CH 4 It is an exothermic reaction and can reach higher CO at lower temperatures. 2 Conversion rate and CH 4 The product is similar to the composition of natural gas used in civil society today and can be directly transported and distributed using existing natural gas pipeline facilities. 2 Conversion into methane is a more feasible CO 2 Transformation and utilization means.

[0004] Because CO 2 Hydromethanation reaction (CO 2 +4H 2 = = CH 4 +2H 2 OΔH θ =-165 kJ / mol) is a highly exothermic reaction, which is not conducive to CO at high temperatures 2 Complete conversion, such as CO at 360℃ 2 The equilibrium conversion rate is reduced to 90%. 2 The main goal of methanation catalysts is to achieve high activity and high CH at low temperatures. 4 Selective.

[0005] Commonly used CO 2Methanation catalysts use Ru, Ni and other active metals, and use silicon oxide, aluminum oxide, cerium oxide and other catalyst carriers. Among them, silicon oxide carrier has high stability and specific surface area, and is an excellent carbon dioxide hydrogenation catalyst carrier, but its inert structure limits its low-temperature activity of loaded Ni-based catalysts. For example, the 3% Ru / TiZrMgAlO x Although the catalyst can be used at a space velocity of 18000-24000L kg -1 h -1 At 310℃, 81% CO 2 Conversion rate and 100% CH 4 Selectivity. 1%Ru / TiO disclosed in CN 111514889A 2 , 1%Ru / Al 2 O 3 The catalyst was heated at a space velocity of 2400 h -1 At 220℃, about 40% CO 2 However, the use of precious metals such as Ru is limited by the high cost and is difficult to achieve industrial application.

[0006] Ni is chosen as the CO 2 Methanation catalyst active metal components are feasible. For example, Ni / TiO 2 Aerogel catalyst at 8000h -1 Space velocity, about 60% CO was obtained at 450℃ 2 The conversion rate and methane selectivity of about 97%. For example, the Ni / TiO 2 The catalyst was heated at 360°C with a space velocity of 15000 h -1 63.5% CO can be obtained 2 Conversion rate.

[0007] CO using nickel as active metal 2 Methanation catalysts often require a higher Ni loading (generally greater than 10wt%), which requires that the catalyst carrier must have a larger specific surface area and higher stability. Mesoporous silica with a high specific surface area and high stability is a commonly used catalyst carrier material. However, traditional mesoporous silica is inherently inert, has weak interactions with metals, and is prone to dust pollution, low yield, and complex synthesis steps. For example, the preparation of mesoporous nano-silica particles disclosed in CN103601201A requires a large amount of water, has a low yield, and has complex synthesis steps. The synthesized nano-silica particles are easily dispersed in the atmosphere, causing dust pollution, which is not conducive to use and storage. Summary of the invention

[0008] In order to overcome the technical problems of conventional nickel-based carbon dioxide hydrogenation catalysts such as small specific surface area, poor catalytic activity, poor selectivity, poor stability, and high manufacturing cost, the present invention provides a rare earth-modified mesoporous silica-supported nickel catalyst. The catalyst has the characteristics of high carbon dioxide hydrogenation activity and high methane selectivity, and the catalyst is in granular form and easy to use and store.

[0009] The technical solution of the present invention is as follows:

[0010] The invention provides a method for preparing a rare earth metal modified mesoporous silica loaded with nickel catalyst, wherein rare earth metal is doped into an amorphous mesoporous silica skeleton by a sol-gel method, the silica is modified, and then metallic nickel is loaded by an impregnation method or a coprecipitation method to obtain a rare earth metal modified mesoporous silica loaded with nickel catalyst.

[0011] Furthermore, the preparation method mainly comprises the following steps:

[0012] (1) dissolving a rare earth metal precursor and a silicon source in an organic solvent to obtain a mixed solution, wherein the organic solvent can simultaneously dissolve the rare earth metal precursor, the silicon source, the pore former and water;

[0013] (2) slowly adding an aqueous solution containing a pore-forming agent to the mixed solution obtained in step (1), stirring until a gel is formed, drying to obtain a xerogel, and subjecting the xerogel to a hydrothermal reaction to obtain a mixture of rare earth-modified mesoporous silica and the pore-forming agent;

[0014] (3) calcining the mixture obtained in step (2) under flowing air conditions to remove the pore-forming agent, thereby obtaining rare earth-modified mesoporous silica;

[0015] (4) dissolving the nickel precursor in a solvent, mixing the mixture evenly with the rare earth-modified mesoporous silica obtained in step (3), removing the solvent, drying, and calcining under flowing air to obtain a rare earth metal-modified mesoporous silica-supported nickel catalyst.

[0016] Furthermore, in step (1), the rare earth metal precursor is one or a combination of two or more of rare earth metal nitrates, chlorides, sulfates, acetylacetonates, and isopropoxides, preferably rare earth metal nitrates; the rare earth metal is one or a combination of two or more of the lanthanide elements, scandium, and yttrium in the periodic table; the silicon source is one or a combination of two or more of tetraethyl orthosilicate, silicic acid, and sodium silicate, preferably tetraethyl orthosilicate; and the organic solvent includes one or a combination of two or more of methanol, ethanol, and propanol, preferably ethanol.

[0017] Furthermore, the mass ratio of the organic solvent to the silicon source in step (1) is 1 to 10, preferably 2 to 6; the molar ratio of silicon to the rare earth metal is 20 to 1000, preferably 50 to 200.

[0018] Furthermore, the pore-forming agent in step (2) is one of triethanolamine, tetraethylammonium hydroxide, tetramethylammonium hydroxide, tripropylamine, or a combination of two or more thereof, preferably triethanolamine and tetraethylammonium hydroxide.

[0019] Furthermore, in step (2), the mass ratio of the silicon source, the pore-forming agent and water in the mixed solution is 1:(0.5-3):(4-8).

[0020] Furthermore, in step (2), the drying temperature is 100 to 150° C., preferably 100 to 110° C., and the drying time is 4 to 48 hours, preferably 12 to 24 hours.

[0021] Furthermore, in step (2), the hydrothermal temperature is 150-200°C, and the hydrothermal time is 1-12 hours; increasing the hydrothermal temperature or extending the hydrothermal time will result in a smaller specific surface area. Preferably, the hydrothermal temperature is 170-180°C, and the hydrothermal time is 3-6 hours.

[0022] Furthermore, in step (3), the calcination temperature is 500-800°C, the heating rate is 0.5-2°C / min, and the calcination time is 8-10h to obtain transparent or translucent block crystals; the calcination conditions are preferably to heat the temperature to 600-700°C at a heating rate of 1-2°C / min and calcine for 8-10h.

[0023] Furthermore, in step (4), the nickel precursor is one of nickel nitrate, nickel chloride, nickel sulfate or nickel acetylacetonate, or a combination of two or more thereof, preferably nickel nitrate; and the solvent is one of water, methanol, ethanol, or a combination of two or more thereof, preferably water.

[0024] Furthermore, in step (4), the calcination temperature is 250-450° C., and the calcination time is 1-10 h.

[0025] Furthermore, the method for loading active metal Ni in step (4) is to grind, granulate and sieve the rare earth modified mesoporous silica into particles of a certain size, and then load Ni using an impregnation method; the impregnation method includes an equal volume impregnation method and an over volume impregnation method.

[0026] Furthermore, in step (4), the loading amount of Ni is 0.1 to 40 wt%, preferably 10 to 20 wt%.

[0027] Another aspect of the present invention provides a rare earth metal modified mesoporous silica supported nickel catalyst prepared by the above preparation method, comprising a rare earth modified amorphous mesoporous silica carrier and supported active metal nickel.

[0028] Furthermore, the specific surface area of ​​the catalyst is 200 to 1000 m 2 / g; the average pore size is 2 to 20 nm.

[0029] Furthermore, the skeleton of the carrier is mainly composed of Si and O, and the rare earth metal is embedded in the skeleton, partially occupying the position of Si; the rare earth metal can affect the pore structure and chemical properties of the carrier, so that it promotes CO 2 Adsorption and activation.

[0030] The present invention also provides the rare earth metal modified mesoporous silica supported nickel catalyst in CO 2 Hydrogenation reduction to CH 4 Application in.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) The rare earth metal-modified mesoporous silica-supported nickel catalyst provided by the present invention has a strong CO 2 Adsorption activation ability, after loading metallic nickel, it synergizes with metallic nickel, has very excellent low-temperature carbon dioxide methanation activity and selectivity, with methane selectivity reaching more than 99%, and has the advantage of good stability.

[0033] (2) The rare earth metal-modified mesoporous silica-supported nickel catalyst of the present invention has a mass fraction of 500 to 800 m 2 / g high specific surface area and good stability, and the finished product is in block form, not easy to float away, easy to use and store. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0035] Figure 1 It is the catalyst support and catalyst N 2 Adsorption isotherms (a) and pore size distribution (b).

[0036] Figure 2 Ni / mSiO 2 (a, b) and Ni / Ce-mSiO 2 (c, d) SEM images (a, c) and TEM images (b, d) of the catalysts.

[0037] Figure 3 The catalyst was tested under the following conditions: CO2 / H 2 / N 2 =19 / 76 / 5, WHSV=24000ml h -1 g -1 CO 2 Conversion rate (a) and CH 4 Selectivity (b). DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0039] Example 1

[0040] The present invention provides a 10Ni / La-mSiO 2 The synthesis method comprises the following steps:

[0041] Dissolve 1.7g of lanthanum nitrate hexahydrate and 42.4g of tetraethyl orthosilicate in 200mL of anhydrous ethanol, and mark this solution as solution A. Take 30.7g of triethanolamine and dissolve it in 23.1g of deionized water to obtain solution B. Add solution B dropwise to solution A under stirring, and then stir to obtain solution C. Then add 43.8g of 25% tetraethylammonium hydroxide aqueous solution dropwise to solution C under stirring, and then stir the mixture at room temperature until a uniform gel is formed. Dry the above gel at 110°C in a blast drying oven for 24h to remove the ethanol and water therein to obtain a dry gel. Put the dry gel into a hydrothermal reactor, heat it to 180°C for 3h, take it out and cool it naturally to room temperature. Then take out the dry gel after the hydrothermal reaction and calcine it in a tubular furnace, pass flowing air, and heat it to 600°C at 2°C / min. After calcination for 8h, La-mSiO 2 Then La-mSiO 2 The particles were crushed and sieved to obtain 160-400 μm particles.

[0042] 10 wt% Ni was loaded into La-mSiO using an equal volume impregnation method. 2 Upper: 2.2g Ni(NO 3 )·6H 2 O was dissolved in 8 mL of deionized water and then added dropwise to 4.0 g of La-mSiO 2The carrier was added until the carrier was completely wetted, and the remaining nickel nitrate solution was added dropwise after the water evaporated. After the water evaporated, it was dried in a blast drying oven overnight, and finally calcined at 350°C in flowing air for 2h to obtain 10Ni / La-mSiO 2 catalyst.

[0043] Example 2

[0044] The present invention provides a preferred Si / Ce=100 10Ni / Ce-mSiO 2 Synthesis method:

[0045] Changing the type and amount of rare earth nitrate, using tetraethyl orthosilicate: cerium nitrate with a molar ratio of 100:1, the rest is the same as Example 1, and 10Ni / Ce-mSiO 2 catalyst.

[0046] Example 3

[0047] The Ni loading was changed to 20wt%, and the rest was the same as in Example 2 to obtain 20Ni / Ce-mSiO 2 catalyst.

[0048] Comparative Example 1

[0049] Without using rare earth nitrate, the rest is the same as Example 1, and 10Ni / mSiO 2 catalyst.

[0050] Comparative Example 2

[0051] Commercial silicon dioxide was used as the catalyst carrier, and the metal Ni was loaded using the same impregnation method as in Example 1 to prepare Ni / SiO 2 catalyst.

[0052] The structural characteristics of the carriers and catalyst samples of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0053] Table 1. Structural properties of carriers and catalyst samples of Examples 1-3 and Comparative Examples 1-2

[0054] sample Ni loading <![CDATA[Specific surface area / m 2 / g]]> Average pore size / nm <![CDATA[Pore volume / cm 2 / g]]> Example 1 Carrier \ 703 3.7 0.75 Example 2 Carrier \ 807 3.1 0.67 Comparative Example 1 Carrier \ 574 4.1 0.72 Example 1 10％ 568 3.6 0.55 Example 2 10％ 687 3.1 0.55 Example 3 20％ 620 3.2 0.49 Comparative Example 1 10％ 553 3.8 0.63 Comparative Example 2 10％ 229 10.1 0.57

[0055] from Figure 1 As can be seen from Table 1, the catalyst synthesized in the present invention has a type IV isotherm adsorption curve (N 2 The adsorption isotherm and H2b type hysteresis loop indicate that the catalyst synthesized in the present invention has a uniform mesoporous structure. From the pore size distribution, it can be seen that the catalyst has a pore size distribution of 2 to 8 nm, which is a typical mesoporous material.

[0056] from Figure 2It can be seen from the SEM and TEM images that the catalyst synthesized by the present invention has a block structure of micrometer size, is not easy to cause dust pollution, and the metal Ni is evenly distributed on the surface of the carrier with a particle size of about 6nm.

[0057] Example 4

[0058] Reaction activity test of the catalysts of Examples 1-3 and Comparative Examples 1-2:

[0059] The activity of the catalysts in Examples 1-3 and Comparative Examples 1-2 was tested in a micro multi-channel fixed bed reactor. 100 mg of the catalyst was mixed with 1.00 g of silicon carbide particles and placed in a quartz tube with an inner diameter of 8 mm. Before the reaction, the catalyst was heated in pure H 2 The catalyst was reduced at 350℃ for 2h, and then the CO 2 Hydrogenation reaction conversion rate and selectivity. The reaction gas composition is 19% CO 2 / 5%N 2 / 76%H 2 , the flow rate is 40mL / min. The composition of the generated gas is detected by online gas chromatography and the CO 2 Conversion rate and CH 4 Selectivity. By increasing the catalyst dosage to 400 mg and adjusting the reaction space velocity to 6000 ml h -1 g -1 , the catalyst in CO 2 CO at 300°C in methanation reaction 2 The results of conversion and selectivity are shown in Table 2.

[0060] Table 2. Catalysts in CO 2 CO at 300°C in methanation reaction 2 Conversion and selectivity

[0061]

[0062] Note: By adjusting the reaction space velocity, the CO 2 Conversion rate and CH 4 Selectivity can be further improved.

[0063] From Table 2 and Figure 3 It can be seen that the Ni / R-mSiO 2 In CO 2 Ni / mSiO has good catalyst activity in methanation reaction without adding rare earth additives 2 The catalyst was heated at 300 °C and the mass space velocity was 24000 ml h -1 g -1 38.3% CO2 Conversion rate, after adding rare earth additive La, under the same conditions, its CO 2 The conversion rate can reach 75.4%, CH 4 The selection performance reaches 99.9%, CH 4 The yield can reach 182.8 mol / (kg·h). 2 It has very good catalytic activity and CH 4 Selective.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Application of a rare earth metal modified mesoporous silica supported nickel catalyst in the production of CH4 by hydrogenation reduction of CO2, characterized in that: The preparation method of the rare earth metal modified mesoporous silica supported nickel catalyst is as follows: rare earth metal is doped into amorphous mesoporous silica by a sol-gel method, and then metal nickel is loaded by an impregnation method or a coprecipitation method to obtain a rare earth metal modified mesoporous silica supported nickel catalyst; the catalyst carrier is rare earth modified mesoporous silica, the active component is nickel, wherein the rare earth metal exists in the form of oxide or anchored in the silica skeleton, the rare earth metal is lanthanum or cerium, and the loading amount of nickel is 0.1-40 wt%; The preparation method comprises the following steps: (1) dissolving a rare earth metal precursor and a silicon source in an organic solvent to obtain a mixed solution; (2) slowly adding an aqueous solution containing a pore-forming agent to the mixed solution obtained in step (1), stirring until a gel is formed, drying to obtain a dry gel, and subjecting the dry gel to a hydrothermal reaction to obtain a mixture of rare earth-modified mesoporous silica and the pore-forming agent; (3) calcining the mixture obtained in step (2) under flowing air conditions to remove the pore-forming agent, thereby obtaining rare earth-modified mesoporous silica; (4) dissolving the nickel precursor in a solvent, mixing the mixture evenly with the rare earth-modified mesoporous silica obtained in step (3), removing the solvent, drying, and calcining the mixture under flowing air to obtain a rare earth metal-modified mesoporous silica-supported nickel catalyst; In step (1), the molar ratio of silicon to rare earth metal is 20-1000; the silicon source is one or a combination of two or more of ethyl orthosilicate, silicic acid, and sodium silicate; The pore-forming agent in step (2) is one of triethanolamine, tetraethylammonium hydroxide, tetramethylammonium hydroxide, tripropylamine, or a combination of two or more thereof; the mass ratio of the silicon source, the pore-forming agent, and water in the mixed solution is 1: (0.5 to 3): (4 to 8); the hydrothermal temperature is 150 to 200°C, and the hydrothermal time is 1 to 12 h; In step (3), the calcination temperature is 500 to 800°C and the calcination time is 8 to 10 h; In step (4), the calcination temperature is 250 to 450°C and the calcination time is 1 to 10 h.

2. The use according to claim 1, characterized in that: In step (1), the rare earth metal precursor is one or a combination of two or more of the rare earth metal nitrate, chloride, sulfate, acetylacetonate, and isopropoxide, and the mass ratio of the organic solvent to the silicon source is 1 to 10.

3. The use according to claim 1, characterized in that: In step (2), the drying temperature is 100 to 150°C and the drying time is 4 to 48 hours.

4. The use according to claim 1, characterized in that: The heating rate in step (3) is 0.5 ~ 2°C / min.

5. The use according to claim 1, characterized in that: The nickel precursor described in step (4) is one of nickel nitrate, nickel chloride, nickel sulfate or nickel acetylacetonate, or a combination of two or more thereof; the solvent is one of water, methanol, and ethanol, or a combination of two or more thereof.

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