A catalyst for efficiently catalyzing carbon dioxide hydrogenation to prepare low-carbon olefins, a preparation method and application thereof

Abstract

The application discloses a kind of catalysts for efficiently catalyzing carbon dioxide hydrogenation to prepare low carbon olefin and preparation method thereof, belong to carbon dioxide recycling technical field.The catalyst includes rare earth metal oxide modified molecular sieve and composite metal oxide loaded on molecular sieve.Metal particles are well dispersed in the catalyst, and the catalyst particle size is smaller.The application obtains rare earth metal oxide modified molecular sieve by isometric impregnation method, then composite metal oxide is loaded on modified molecular sieve by coprecipitation method and one-pot method, and the obtained catalyst is used in carbon dioxide hydrogenation to prepare C2-C4 olefin reaction, carbon dioxide conversion rate reaches more than 20%, low carbon olefin (C2-C4 olefin) selectivity reaches more than 80%, especially propylene selectivity is higher, and can reach 50%.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide recycling technology, and in particular to a highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins, its preparation method, and its application. Background Technology

[0002] In recent years, the utilization of carbon dioxide has attracted the attention of researchers in the global chemical and environmental protection fields. Low-carbon olefins, especially ethylene and propylene, are the most important and fundamental chemical raw materials for organic material synthesis, and their output is one of the important indicators for measuring the development level of a country's chemical industry. The production of low-carbon olefins by CO2 hydrogenation is not only an effective way to utilize CO2 resources, but also a new non-petroleum route for producing ethylene, propylene, and other low-carbon olefins. This has profound and significant strategic importance for alleviating the greenhouse effect and energy crisis. However, problems still exist, such as poor CO2 conversion rate, poor selectivity and stability of low-carbon olefins, and unclear interactions with additives. The production process of producing low-carbon olefins by CO2 hydrogenation has not yet been applied to industrial production, mainly due to the low single-pass CO2 conversion rate of the catalyst, low olefin selectivity, the presence of large amounts of carbon monoxide and alkanes in the products, and the poor stability and short lifespan of the catalyst during the reaction. Therefore, researching a catalyst for the production of low-carbon olefins by CO2 hydrogenation is of great significance.

[0003] CN106423263A discloses a catalyst for the preparation of low-carbon olefins by carbon dioxide hydrogenation and the synthesis of low-carbon olefins. It uses a composite of Zn-Zr oxide and molecular sieve. The selectivity of low-carbon olefins in CO2 hydrogenation is relatively high, but the CO2 conversion rate is only 10% and the selectivity of low-carbon olefins is 80%.

[0004] CN201510116355B discloses an iron-based catalyst for the hydrogenation of CO2 to produce low-carbon olefins, its preparation, and its application. This patent reports the use of an Fe3O4 catalyst with added oxide promoters. While the CO2 conversion rate is high in the CO2 hydrogenation reaction, the selectivity for low-carbon olefins is only 28%.

[0005] CN108620089A discloses a catalyst for the hydrogenation of carbon dioxide to low-carbon olefins, its preparation method, and its application. The catalyst is Fe3O4 nanospheres with a manganese additive supported on the surface, the loading of which is 5–20% wt. The reaction is carried out at a temperature of 350 °C and a reaction space velocity of 4000 h⁻¹. -1 At that time, the CO2 conversion rate reached 44.7%, the selectivity for C2-C4 olefins was 46.2%, and the selectivity for byproducts CO and CH4 was 9.3% and 22%, respectively.

[0006] The catalysts provided by the above inventions have the disadvantages of low CO2 conversion rate, low selectivity for low-carbon olefins, harsh reaction conditions, and poor stability. Summary of the Invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins, its preparation method, and its application. The catalyst has well-dispersed metal particles and smaller particle size, exhibiting excellent catalytic performance in the hydrogenation of carbon dioxide to produce low-carbon olefins, especially for propylene, with a selectivity of up to 50%.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins, comprising a molecular sieve modified with rare earth metal oxides and a composite metal oxide supported on the molecular sieve.

[0010] In the highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins described in this invention, the composite metal oxide can form a solid solution structure with a high concentration of oxygen holes on the surface, which is beneficial for CO2 adsorption and the generation of low-carbon olefins.

[0011] The particle size of the catalyst for the efficient catalytic hydrogenation of carbon dioxide to produce low-carbon olefins is preferably 10-60 mesh; more preferably 40-60 mesh.

[0012] The above catalyst, by mass percentage, includes the following components:

[0013] Composite metal oxides: 20%–70%;

[0014] Molecular sieves modified with rare earth metal oxides: 30%–80%.

[0015] Preferably, the rare earth metal oxide is selected from one or more of CeO2, La2O3, Nd2O3, Dy2O3, and Eu2O3; more preferably, it is CeO2 or La2O3.

[0016] Preferably, the molecular sieve is an acidic molecular sieve.

[0017] Preferably, the acidic molecular sieve is selected from one or more of SAPO-34, HZSM-5, and HY molecular sieves; more preferably, it is SAPO-34 molecular sieve.

[0018] Preferably, the mass ratio of the rare earth metal oxide to the molecular sieve is (2-6):(30-80). In some specific embodiments of the present invention, the mass ratio of the rare earth metal oxide to the molecular sieve is 3:20.

[0019] Preferably, the composite metal oxide is selected from two or more of ZrO2, ZnO, MnO2, InO2, and Ga2O3; more preferably, it is any combination of two of ZrO2, ZnO, MnO2, InO2, and Ga2O3. In some specific embodiments of the present invention, the composite metal oxide is selected from ZrO2 and ZnO.

[0020] Preferably, the mass ratio of the molecular sieve modified with the composite metal oxide and rare earth metal oxide is (1-8):(8-1). In some specific embodiments of the present invention, the preferred mass ratio of the molecular sieve modified with the composite metal oxide and rare earth metal oxide is (2-7):(3-8).

[0021] This invention also provides a method for preparing a highly efficient catalyst for the catalytic hydrogenation of carbon dioxide to produce low-carbon olefins, comprising the following steps:

[0022] 1) Rare earth metal oxide precursors are loaded onto molecular sieves by an equal-volume impregnation method and then dried to obtain modified molecular sieve precursors.

[0023] 2) Mix the mixed metal salt solution containing the composite metal oxide precursor with the modified molecular sieve precursor obtained in step 1), add an alkaline precipitant to form a precipitate, and then calcine the precipitate to finally obtain a highly efficient catalyst for the hydrogenation of carbon dioxide to prepare low-carbon olefins.

[0024] In the above preparation method, the composite metal oxide precursor is preferably Zr. 4+ Zn 2+ Mn 4+ In 4+ Ga 3+ Two or more of the soluble salts.

[0025] The catalyst was prepared using a co-precipitation method and a one-pot method. This reduces the agglomeration of the active components caused by multiple calcinations, and improves the stability and selectivity of the catalyst for the efficient catalytic hydrogenation of carbon dioxide to low-carbon olefins.

[0026] Preferably, the rare earth metal oxide precursor of the present invention is selected from Ce. 4+ La 3+ 、Nd 3+ Dy 3+ Eu 3+ One or more of the soluble salts of; more preferably Ce 4+ Or La 3+ Soluble salts.

[0027] Preferably, the concentration of the metal salt in the mixed metal salt solution is 0.1 to 1 mol / L.

[0028] Preferably, the solvent in the mixed metal salt solution is selected from ethanol and water.

[0029] Preferably, the dissolution temperature of the composite metal oxide precursor is 35℃~80℃.

[0030] The addition of an alkaline precipitant makes the pH of the mixed system 9-10, and the composite metal oxide ions co-precipitate to form hydroxide precipitates.

[0031] The molar ratio of metal ions to alkaline precipitant in the above-mentioned mixed metal salt solution is 1:(0.5-10); more preferably 1:(0.5-6). In a specific embodiment of the present invention, the molar ratio of metal ions to alkaline precipitant in the mixed metal salt solution is preferably 1:2.5.

[0032] The alkaline precipitant is selected from one or more of ammonia, sodium hydroxide, water-soluble carbonates, and water-soluble bicarbonates.

[0033] When the composite metal oxide precursor is selected from Zr 4+ and Zn 2+ When Zr is a soluble salt, 4+ and Zn 2+ The preferred molar ratio is (1.5–5):1. In some specific embodiments of the present invention, the Zr... 4+ and Zn 2+ The preferred molar ratio is 2:1.

[0034] In this invention, when the composite metal oxide is selected from ZnO and ZrO2, the ZnO content is preferably 15wt% to 58wt%, and the ZrO2 content is preferably 42wt% to 75wt%.

[0035] In this invention, the precipitate in step 2) undergoes post-treatment such as precipitation aging, washing, drying, and grinding before calcination.

[0036] The preferred precipitation aging time is 0.5 to 5 hours.

[0037] The present invention does not have any particular limitation on the washing solution described above, and can be any washing solvent known to those skilled in the art.

[0038] In some specific embodiments of the present invention, the washing solvent is selected from deionized water, and the washing is performed until the pH is 6-8.

[0039] The present invention does not specifically limit the above-mentioned drying method, and can use methods well known to those skilled in the art such as vacuum drying, reduced pressure drying, and heating drying.

[0040] In some specific embodiments of the present invention, the drying is carried out by heating, and the heating temperature is preferably 50℃~80℃.

[0041] After precipitation, aging, washing, and drying, the precipitate is ground and then calcined to obtain the highly efficient catalyst for the hydrogenation of carbon dioxide to prepare low-carbon olefins as described in this invention.

[0042] The preferred grinding time is 1 to 5 hours.

[0043] The aforementioned composite metal oxide precursor is precipitated by calcination to generate the composite metal oxide.

[0044] The roasting temperature is preferably 300℃~700℃; more preferably 400℃~600℃.

[0045] The roasting time is preferably 1 to 20 hours; more preferably 3 to 10 hours.

[0046] The catalyst described in this invention requires activation pretreatment before use. The specific steps are as follows:

[0047] The catalyst prepared above is loaded into the reactor, treated with an inert atmosphere, and then the reaction pressure is increased to the required reaction pressure. The atmosphere of the reactants is then switched to carry out the reaction.

[0048] The preferred temperature for the activation pretreatment is 300℃ to 600℃, and the preferred pretreatment time is 0.5 to 5 hours.

[0049] The catalyst described in this invention is stable and can be used to catalyze the hydrogenation reaction of carbon dioxide, achieving a CO2 conversion rate of over 20% and a selectivity of over 80% for low-carbon olefins (C2-C4 olefins).

[0050] When the catalyst described in this invention is used in the reaction of CO2 hydrogenation to synthesize propylene, the propylene obtained has a high selectivity, reaching 50%.

[0051] The above catalyst was applied to the reaction of CO2 hydrogenation to synthesize propylene, using CO2 and H2 as raw materials to synthesize propylene.

[0052] The reaction of CO2 hydrogenation to synthesize propylene includes the following pretreatment: placing the catalyst under an inert gas (including but not limited to nitrogen) for pretreatment at a temperature of 300-600°C for a time of 0.5-5 hours.

[0053] The reaction conditions for the synthesis of propylene by CO2 hydrogenation include: a preferred reaction pressure of 1–5 MPa, a preferred reaction temperature of 350–600 °C, and a preferred feed space velocity of 2000 h⁻¹. -1 ~12000h -1The preferred molar ratio of hydrogen to carbon dioxide is (2-4):1.

[0054] The inert atmosphere is preferably nitrogen and / or argon.

[0055] Compared with existing technologies, the highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins provided by this invention comprises a molecular sieve modified with rare-earth metal oxides and a composite metal oxide supported on the molecular sieve. The catalyst exhibits good metal particle dispersion and smaller particle size. This invention obtains the molecular sieve modified with rare-earth metal oxides through an equal-volume impregnation method, and then loads the composite metal oxide onto the modified molecular sieve through a co-precipitation method and a one-pot method. The resulting catalyst, used in the hydrogenation of carbon dioxide to produce C2-C4 olefins, achieves a carbon dioxide conversion rate of over 20% and a selectivity for low-carbon olefins (C2-C4 olefins) of over 80%, with particularly high selectivity for propylene, reaching 50%. Detailed Implementation

[0056] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, describes the highly efficient catalyst for the catalytic hydrogenation of carbon dioxide to produce low-carbon olefins, its preparation method, and its applications.

[0057] Example 1

[0058] (1) Catalyst preparation

[0059] 2.15 g of lanthanum nitrate was dissolved in 5.43 g of water, and then 13.81 g of SAPO-34 molecular sieve was added. The lanthanum nitrate was directly deposited onto the SAPO-34 molecular sieve by drying at 120 °C to obtain a modified molecular sieve precursor, material a.

[0060] 46.8g of zirconium nitrate (industrial grade) powder was dispersed in 300g of water. 200g of zinc nitrate aqueous solution (containing 7.8g of zinc element) was added to the above solution and dissolved completely. Then, material a was added to the mixed metal salt solution and mixed evenly. 200g of ammonia aqueous solution (0.1mmol / mL) was added dropwise to the above system, controlling the pH of the system at 9-10, so that zirconium and zinc co-precipitate. The precipitation was then aged, filtered, washed with water until the pH was 6-8, dried, and finally calcined at 300℃ for 4h in air atmosphere. After natural cooling, it was ground evenly, pressed into tablets at 15MPa, crushed, and sieved into 40-60 mesh particles to obtain the catalyst.

[0061] (2) Synthesis of propylene

[0062] In a fixed-bed reactor, the reaction temperature was 380℃, the reaction pressure was 3MPa, the molar ratio of H2:CO2:N2 was 73:24:3, and the GHSV was 4500h. -1Before introducing the raw materials H2, CO2, and N2, the catalyst prepared in step (1) is treated in an N2 atmosphere at 380°C for 1 hour.

[0063] Example 2

[0064] (1) Catalyst preparation

[0065] 46.8 g of zirconium nitrate (industrial grade) powder was dispersed in 300 g of water. 200 g of zinc nitrate aqueous solution (containing 21.6 g of zinc) was added to the above solution and dissolved thoroughly. Then, material a from Example 1 was added to the mixed metal salt solution and mixed evenly. 200 g of ammonia solution (0.1 mmol / mL) was added dropwise to the above system, controlling the pH of the system at 9-10, so that zirconium and zinc co-precipitate. The precipitate was then aged, filtered, washed with water until the pH reached 6-8, dried, and calcined at 300°C for 4 hours in air atmosphere, and naturally cooled to obtain catalyst M. The catalyst was then ground evenly, pressed into tablets at 15 MPa, crushed, and sieved into 40-60 mesh particles to obtain the catalyst.

[0066] (2) Synthesis of propylene

[0067] The reaction temperature in the fixed-bed reactor was 380℃, the reaction pressure was 3MPa, the molar ratio of H2:CO2:N2 was 73:24:3, and the GHSV was 4500h. -1 Before introducing the raw materials H2, CO2, and N2, the catalyst prepared in step (1) is treated in an N2 atmosphere at 380°C for 1 hour.

[0068] Example 3

[0069] (1) Catalyst preparation

[0070] 500g of zirconium nitrate and zinc nitrate aqueous solution (containing 34.5g of zirconium and 21.6g of zinc) and 200g of ammonia solution (0.1mmol / mL) were added dropwise to the above system, controlling the pH of the system at 9-10, so that the zirconium and zinc elements would co-precipitate. Then, material a described in Example 1 was added to the mixed metal salt solution and mixed evenly. The precipitate was aged, filtered, washed with water until the pH was 6-8, dried, calcined at 500°C for 4 hours in air atmosphere, and after natural cooling, ground evenly. The precipitate was then pressed into tablets, crushed, and sieved into 40-60 mesh particles under 15MPa to obtain the catalyst.

[0071] (2) Synthesis of propylene

[0072] In a fixed-bed reactor, the reaction temperature was 380℃, the reaction pressure was 3MPa, the molar ratio of H2:CO2:N2 was 73:24:3, and the GHSV was 4500h. -1Before introducing the raw materials H2, CO2, and N2, the catalyst prepared in step (1) is treated in an N2 atmosphere at 380°C for 1 hour.

[0073] Example 4

[0074] (1) Catalyst preparation

[0075] 500g of zirconium nitrate and zinc nitrate aqueous solution (containing 34.5g of zirconium and 21.6g of zinc) was mixed evenly with material a described in Example 1. 200g of ammonia solution (0.1mmol / mL) was added dropwise to the above system, and the pH of the system was controlled at 9-10 to allow the zirconium and zinc to co-precipitate. The precipitate was then aged, filtered, washed with water until the pH reached 6-8, dried, and finally calcined at 500°C for 4 hours in air. After natural cooling, the precipitate was pressed into tablets, crushed, and sieved into 40-60 mesh particles under 15MPa to obtain the catalyst.

[0076] (2) Synthesis of propylene

[0077] In a fixed-bed reactor, the reaction temperature was 380℃, the reaction pressure was 3MPa, the molar ratio of H2:CO2:N2 was 73:24:3, and the GHSV was 4500h. -1 Before introducing the raw materials H2, CO2, and N2, the catalyst prepared in step (1) is treated in an N2 atmosphere at 380°C for 1 hour.

[0078] Example 5

[0079] (1) Catalyst preparation

[0080] 500g of zirconium nitrate and zinc nitrate aqueous solution (containing 34.5g of zirconium and 48.6g of zinc) was mixed evenly with material a described in Example 1. 200g of ammonia aqueous solution (0.1mmol / mL) was added dropwise to the above system, and the pH of the system was controlled at 9-10 to allow the elemental zirconium and zinc to co-precipitate. Then, the precipitation was aged, filtered, washed with water until the pH was 6-8, dried, and finally calcined at 600°C for 3 hours in air atmosphere. After natural cooling, it was ground evenly, pressed into tablets at 15MPa, crushed, and sieved into 40-60 mesh particles to obtain the catalyst.

[0081] (2) Synthesis of propylene

[0082] The reaction temperature in the fixed-bed reactor was 380℃, the reaction pressure was 3MPa, the molar ratio of H2:CO2:N2 was 73:24:3, and the GHSV was 4500h. -1 Before introducing the raw materials H2, CO2, and N2, the catalyst prepared in step (1) is treated in an N2 atmosphere at 380°C for 1 hour.

[0083] Comparative Example 1

[0084] (1) Catalyst preparation

[0085] Compared with Example 1, no rare earth metals were added to the SAPO-34 molecular sieve for modification, but everything else was the same as in Example 1. The catalyst was prepared with a particle size of 40-60 mesh.

[0086] (2) Synthesis of propylene

[0087] Before the reaction, the catalyst prepared in step (1) was pretreated at 380℃ and 0.5MPa with N2 for 1h. After the pretreatment, the feed gas (H2 / CO2 / N2 (molar ratio: 73 / 24 / 3) was switched, and the temperature controller and back pressure valve were adjusted to bring the reaction temperature and pressure to 380℃ and 3.0MPa, respectively. The flow rate of the mass flow meter was adjusted to 150mL / min (standard conditions). After the temperature and pressure stabilized, the reaction was started to produce propylene by carbon dioxide hydrogenation.

[0088] The testing method is as follows:

[0089] Online Gas Chromatograph 1: Equipped with a TDX-01 packed column, TCD thermal conductivity detector, and gas injection valve. Used for the analysis of gases such as H2, CO, CH4, and CO2 in gaseous products.

[0090] Online Gas Chromatograph 2: Equipped with an alumina packed column, FID detector, and gas injection valve. Used for the analysis of alkanes and low-carbon olefins in gas phase products.

[0091] Table 1 Performance tests of the catalysts prepared in Examples 1-5 and Comparative Example 1

[0092]

[0093] Note: C2 0 -C4 0 Alkane products with 2 to 4 carbon atoms; C2-C4 ＝ For olefin products with 2 to 4 carbon atoms; C3 ＝ It is a propylene product; C5 + Alkane products with ≥5 carbon atoms; O / P indicates the molar ratio of alkene to alkane.

[0094] As can be seen from the above examples and comparative data, in the reaction process of carbon dioxide hydrogenation, the catalyst has high C2-C4 olefin selectivity (up to 88%) and propylene selectivity of over 50%, which is of great significance for the efficient preparation of C2-C4 olefins, especially propylene, by carbon dioxide hydrogenation.

[0095] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins, characterized in that, Includes the following steps: 1) Rare earth metal oxide precursors are loaded onto molecular sieves by an equal-volume impregnation method and then dried to obtain modified molecular sieve precursors; The rare earth metal oxide precursor is selected from La 3+ Soluble salts; the molecules are selected from acidic molecular sieves, and the acidic molecular sieves are selected from SAPO-34; 2) Mix the mixed metal salt solution containing the composite metal oxide precursor with the modified molecular sieve precursor obtained in step 1), add an alkaline precipitant to form a precipitate, then calcine the precipitate to finally obtain a highly efficient catalyst for the hydrogenation of carbon dioxide to prepare low-carbon olefins. The composite metal oxide precursor is selected from Zr. 4+ and Zn 2+ Soluble salts.

2. The method for preparing the highly efficient catalyst for the hydrogenation of carbon dioxide to low-carbon olefins according to claim 1, characterized in that, The concentration of the metal salt in the mixed metal salt solution in step 2) is 0.1~1 mol / L; The molar ratio of the metal salt to the alkaline precipitant in the mixed metal salt solution is 1:(0.5~10).

3. The method for preparing the highly efficient catalyst for the hydrogenation of carbon dioxide to low-carbon olefins according to claim 1, characterized in that, The Zr 4+ and Zn 2+ The molar ratio is (1.5~5):

1.

4. A highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins, characterized in that, The catalyst is prepared according to any one of claims 1 to 3; the catalyst comprises a molecular sieve modified with rare earth metal oxide and a composite metal oxide supported on the molecular sieve; the rare earth metal oxide is selected from La2O3; the molecular sieve is selected from acidic molecular sieve, and the acidic molecular sieve is selected from SAPO-34; the composite metal oxide is selected from ZrO2 and ZnO.

5. The highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins according to claim 4, characterized in that, The mass ratio of the rare earth metal oxide to the molecular sieve is (2~6):(30~80).

6. The highly efficient catalyst for the hydrogenation of carbon dioxide to produce low-carbon olefins according to claim 4, characterized in that, The mass ratio of the molecular sieve modified with composite metal oxide and rare earth metal oxide is (1~8):(8~1).

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