A catalyst suitable for the hydrogenation of carbon dioxide to higher hydrocarbons, its preparation method and application

Abstract

The present invention provides a catalyst suitable for catalytic hydrogenation of carbon dioxide to higher hydrocarbons, its preparation method and application. The preparation of the catalyst is as follows: an iron source, oxalic acid and alumina are uniformly mixed and then added to a mortar for grinding by room-temperature solid-phase reaction method to obtain a catalyst precursor. Then it is dried and calcined to become a red solid, and an iron-based catalyst supported on alumina is obtained. Then a soluble salt of metal M is introduced into the iron-based catalyst supported on alumina, which can be introduced by incipient wetness impregnation method or directly introduced by mixing the soluble salt of metal M, the iron source, oxalic acid and alumina together and carrying out the room-temperature solid-phase reaction method; the metal M is any one or more of Zn, K, Co, and Cu. The present invention can simply and effectively load the active components on the alumina support, improve the dispersion degree of the active components, has higher activity than the traditional impregnation method, has a simple operation process, saves time, and avoids the generation of waste water.

Description

Technical Field

[0001] The present invention relates to a catalyst suitable for catalytic hydrogenation of carbon dioxide to higher hydrocarbons, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing annual emissions of CO 2 and the increasingly serious greenhouse effect, catalytic hydrogenation of CO 2 can convert cheap and abundant CO 2 into hydrocarbon products with added value, which is one of the effective ways to solve the greenhouse effect and achieve sustainable economic development. Among them, iron-based catalysts are widely used due to their good ability of CO 2 hydrogenation to hydrocarbons. Patent CN105289610A provides a method for preparing an alumina-supported iron-based catalyst by an impregnation method and its application in organic wastewater treatment. This method reduces the agglomeration of active components on the carrier and increases the stability of the catalyst; the disadvantage is that wastewater is generated during the preparation process and the preparation process is complex.

[0003] There are few reports on the use of CO 2 hydrogenation for the preparation of long-chain hydrocarbons. Patent CN114870886A provides a preparation method of a ZSM-5 supported iron-sodium catalyst and its application in CO 2 hydrogenation to higher hydrocarbons. The advantage of this catalyst is that the selectivity of CH 4 is only 2.1%, and the selectivity of carbon hydrocarbons reaches 68.5%. The disadvantage is that the conversion rate of CO 2 is only 22.4%, and wastewater is also generated during the process, polluting the environment.

[0004] Patent CN113351207A provides a preparation method of a catalyst for CO 2 hydrogenation to prepare liquid fuels. The preparation process of this catalyst by hydrothermal synthesis is complex, the preparation time is long, and a large amount of wastewater is generated. Although it has a relatively high CO 2 conversion rate (above 28%) and a relatively low CO selectivity (below 18.9%), the highest selectivity of C 5 + is below 42.5%. Patent CN113649010A provides a method for preparing an iron-based catalyst by a dry chemical method and a vacuum-microwave heating method, which can quickly synthesize a uniformly dispersed supported iron-based catalyst. The CO 2 conversion rate of this catalyst in CO 2 hydrogenation is 42.2%. The disadvantage of this method is that vacuum-microwave heating is required, and the conditions are relatively harsh. Summary of the Invention

[0005] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a catalyst suitable for catalytic hydrogenation of carbon dioxide to higher hydrocarbons, its preparation method and application. A method for preparing an alumina-supported iron-based catalyst by room-temperature solid-phase reaction and a catalyst modified with other additives are designed. The catalyst is prepared by room-temperature solid-phase reaction, so that iron oxalate is loaded on alumina during the synthesis process, which not only avoids the generation of wastewater, has a simple preparation process and low cost, but also has a high dispersion degree of active components on the carrier, effectively avoiding the agglomeration of active components. The catalyst has excellent performance and has a high CO 2 conversion rate, and in the product distribution, the selectivity of C 5+ hydrocarbons can reach 84.78%.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The preparation method of a catalyst suitable for catalytic hydrogenation of carbon dioxide to higher hydrocarbons includes the following steps:

[0008] 1) Alumina, oxalic acid dihydrate and an iron source are added to a mortar and mixed evenly, and then ground until a yellow viscous substance or powdery substance is formed to obtain a catalyst precursor; wherein, the iron source is one or more of iron(III) nitrate nonahydrate, iron(III) acetylacetonate, and iron(III) citrate;

[0009] 2) The catalyst precursor obtained in step 1) is dried and then calcined in an air atmosphere at 300-600 °C for 1-6 h to obtain the catalyst suitable for CO 2 hydrogenation to higher hydrocarbons.

[0010] The present invention can simply and effectively load the active components on the alumina carrier, improve the dispersion degree of the active components, has higher activity than the traditional impregnation method, has a simple operation process, saves time, and avoids the generation of wastewater.

[0011] Further, in step 1), the mass ratio of the alumina to the oxalic acid dihydrate is 1:0.05-0.6, preferably 1:0.3-0.4; in step 1), the mass ratio of the alumina to the Fe element in the iron source is 1:0.05-0.5, preferably 1:0.1-0.2.

[0012] Further, in step 2), the drying temperature is 50-120 °C and the time is 1-8 h.

[0013] Further, the finally prepared catalyst in step 2) is also doped with a metal element M. The soluble salt of metal M can be introduced into the alumina-supported iron-based catalyst by incipient wetness impregnation method or directly by mixing the soluble salt of metal M, iron(III) nitrate, oxalic acid and alumina and carrying out room-temperature solid-phase reaction method. The preparation method is one of the following:

[0014] Method 1: A soluble salt of metal M is further added to the mortar in step 1), and then it is successively ground, dried, and calcined in an air atmosphere to finally obtain a catalyst doped with metal element M.

[0015] Method 2: The soluble salt of metal M is dissolved in deionized water, and is added dropwise to the catalyst precursor obtained in step 1) by the equal-volume impregnation method for full impregnation, and then successively dried and calcined in an air atmosphere to finally obtain a catalyst doped with metal element M.

[0016] Furthermore, the metal element M is any one or more of Zn, K, Co, and Cu, and the soluble salt of metal M is its nitrate.

[0017] Furthermore, the mass of the doped metal element M is 1-20% of the mass of the alumina raw material, preferably 9-15%.

[0018] The application of the catalyst described in the present invention in the hydrogenation of carbon dioxide to produce higher hydrocarbons, and its application method is: a catalytic reaction is carried out in a fixed bed reactor, the catalyst is installed in the isothermal section of the fixed bed reactor, and H 2 is introduced and reduced at 300-500 °C for 4-12 h, then the reaction temperature is adjusted to 260-400 °C, the reaction pressure is 1-7 MPa, the reaction volume space velocity is 1500-8000 h -1 , H 2 / CO 2 The molar ratio is 2-3:1, and the hydrogenation of carbon dioxide to produce higher hydrocarbons is carried out.

[0019] Furthermore, the higher hydrocarbons are hydrocarbon substances with no less than 5 carbon atoms.

[0020] Compared with the prior art, the main advantages of the present invention include:

[0021] Compared with the existing CO 2 hydrogenation catalyst, this catalyst is prepared by the room temperature solid-phase reaction method by uniformly mixing one or more of iron sources (ferric nitrate nonahydrate, iron acetylacetonate, ferric citrate), oxalic acid and alumina, and at the same time introducing an auxiliary agent (metal M). The obtained catalyst has a large specific surface area, not only avoids the generation of waste water, has a simple preparation process and low cost, but also has a high dispersion degree of the active component on the carrier, effectively avoiding the agglomeration of the active component. And it shows good catalytic performance in the hydrogenation reaction of carbon dioxide. The CO 2 conversion rate of the obtained catalyst can reach 34.74%, the selectivity to the target product C 5 + hydrocarbon can reach 83.31%, and the selectivity to CH 4 can be reduced to 9.36%. Description of the Drawings

[0022] Figure 1 XRD images of iron oxalate catalysts supported on alumina with different addition methods. Specific implementation mode

[0023] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0024] Example 1

[0025] Taking TDO / A as an example, its preparation method is as follows:

[0026] 2.17 g of Fe(NO) 3 ·9H 2 O, 1.02 g of oxalic acid dihydrate, and 2.99 g of alumina were added to a 50 mL mortar. After mixing evenly, it was ground for 40 min until the sample became a yellow viscous substance. Then it was dried at 60 °C for 6 hours to obtain the TDO / A precursor.

[0027] The obtained catalyst precursor was then heated to 400 °C (heating rate: 5 °C / min) in an air atmosphere, and then calcined at a constant temperature for 2 hours to obtain the final product TDO / A catalyst, and the XRD is as Figure 1 shown.

[0028] Comparative Example 1

[0029] Taking YXT / A as an example, its preparation method is as follows:

[0030] 1.89 g of iron acetylacetonate and 2.99 g of alumina were added to a 50 mL mortar. After mixing evenly, it was ground for 40 min until the sample became a powdery substance to obtain the YXT / A precursor.

[0031] The obtained catalyst precursor was then heated to 400 °C (heating rate: 5 °C / min) in an air atmosphere, and then calcined at a constant temperature for 2 hours to obtain the final product XST / A catalyst.

[0032] Comparative Example 2

[0033] Taking WDO / A as an example, its preparation method is as follows:

[0034] 2.17 g of Fe(NO) 3 ·9H 2 O and 1.02 g of oxalic acid dihydrate were added to a 50 mL mortar. After mixing evenly, it was ground for 40 min until the sample became yellow and viscous, and then 2.99 g of alumina was added and ground for another 30 min. Then it was dried at 60 °C for 6 hours to obtain the WDO / A precursor.

[0035] The obtained catalyst precursor was then calcined in an air atmosphere at 400 °C (heating rate: 5 °C / min) for 2 hours to obtain the final product WDO / A catalyst, and the XRD is as shown in Figure 1 shown.

[0036] Comparative Example 3

[0037] Taking DDO / A as an example, its preparation method is as follows:

[0038] 2.17 g of Fe(NO) 3 ·9H 2 O and 1.02 g of oxalic acid dihydrate were added to a 50 mL mortar, mixed evenly and ground for 40 min until the sample became yellow and viscous. Then it was dried at 60 °C for 6 hours, and then 2.99 g of alumina was added and ground for another 30 min to obtain the DDO / A precursor.

[0039] The obtained catalyst precursor was then calcined in an air atmosphere at 400 °C (heating rate: 5 °C / min) for 2 hours to obtain the final product DDO / A catalyst, and the XRD is as shown in Figure 1 shown.

[0040] Example 2

[0041] Taking YXT+TDO / A as an example, its preparation method is as follows:

[0042] 2.17 g of Fe(NO) 3 ·9H 2 O, 1.02 g of oxalic acid dihydrate, 1.89 g of iron acetylacetonate and 2.99 g of alumina were added to a 50 mL mortar, mixed evenly and ground for 40 min until the sample became viscous. Then it was dried at 60 °C for 6 hours to obtain the YXT+TDO / A precursor.

[0043] The obtained catalyst precursor was then heated to 400 °C (heating rate: 5 °C / min) in an air atmosphere, and then calcined at a constant temperature for 2 hours to obtain the final product YXT+TDO / A catalyst.

[0044] Example 3

[0045] The preparation method of the 0.02Cu-0.04K-TDO / A catalyst is as follows:

[0046] 0.38 g of Cu(NO 3 ) 2 ·6H 2 O and 0.52 g of KNO 3Dissolve it in 5 ml of deionized water solution, and then dropwise add the mixed solution of copper nitrate and potassium nitrate to 5 g of the catalyst precursor TDO / A in Example 1. After impregnating at room temperature for 12 hours, dry it at 60 °C.

[0047] Then heat the obtained catalyst precursor to 400 °C in a nitrogen atmosphere (heating rate is 5 °C / min), and then keep it at a constant temperature and calcine for 2 hours to obtain the final product, 0.02Cu-0.04K-TDO / A catalyst.

[0048] Example 4

[0049] The preparation method of 0.01Zn-0.04Cu-0.04KN-TDO / A catalyst is as follows:

[0050] Put 0.23 g of Zn(NO 3 ) 2 ·3H 2 O, 0.76 g of Cu(NO 3 ) 2 ·6H 2 O, 0.52 g of KNO 3 , 2.17 g of Fe(NO) 3 ·9H 2 O, 1.02 g of oxalic acid dihydrate, and 2.99 g of alumina into a 50 mL mortar. After mixing evenly, grind for 40 min, and then dry at 60 °C for 6 hours to obtain the 0.01Zn-0.04Cu-0.04KN-TDO / A precursor.

[0051] Then heat the obtained catalyst precursor to 400 °C in an air atmosphere (heating rate is 5 °C / min), and then keep it at a constant temperature and calcine for 2 hours to obtain the final product, 0.01Zn-0.04Cu-0.04KN-TDO / A catalyst.

[0052] Example 5

[0053] The preparation method of 0.01Co-0.04Cu-0.04KN-TDO / A catalyst is as follows:

[0054] Put 0.245 g of Co(NO 3 ) 2 ·6H 2 O, 0.76 g of Cu(NO 3 ) 2 ·6H 2 O, 0.52 g of KNO 3 , 2.17 g of Fe(NO) 3 ·9H 2O, 1.02 g of oxalic acid dihydrate, and 2.99 g of aluminum oxide were added to a 50 mL mortar, mixed evenly, and ground for 40 min. Then, the precursor was dried at 60 °C for 6 hours to obtain a 0.01Co-0.04Cu-0.04KN-TDO / A precursor.

[0055] The obtained catalyst precursor was then heated to 400° C. (heating rate of 5° C. / min) in an air atmosphere, and then calcined at a constant temperature for 2 hours to obtain the final product 0.01Co-0.04Cu-0.04KN-TDO / A catalyst.

[0056] Example 6

[0057] The preparation method of 0.04Cu-0.04KN-TDO / A catalyst is as follows:

[0058] 0.76 g Cu(NO 3 ) 2 6H 2 O, 0.52g KNO 3 , 2.17 g of Fe(NO) 3 9H 2 O, 1.02 g of oxalic acid dihydrate, and 2.99 g of aluminum oxide were added into a 50 mL mortar, mixed evenly, and ground for 40 min. Then, the precursor 0.04Cu-0.04KN-TDO / A was obtained after drying at 60 °C for 6 hours.

[0059] The obtained catalyst precursor was then heated to 400° C. (heating rate of 5° C. / min) in an air atmosphere, and then calcined at a constant temperature for 2 hours to obtain the final product 0.04Cu-0.04KN-TDO / A catalyst.

[0060] The catalysts of Examples 1 to 7 were evaluated for their carbon dioxide hydrogenation activity. The performance evaluation was performed on a fixed bed experimental device. The catalysts were installed in the constant temperature section of the fixed bed reactor and heated under H 2 Atmosphere, airspeed 3000h -1 The reaction was reduced at 400 °C for 9 h, and then the reaction temperature was adjusted to 340 °C, the pressure to 3 MPa, and the reaction volume space velocity to 3000 h -1 , H 2 / CO 2 The molar ratio is 3:1, and carbon dioxide is hydrogenated to produce higher carbon hydrocarbons.

[0061] Table 1

[0062]

[0063] From Table 1 above, we can get the following conclusions:

[0064] 1) Compared with Examples 1-2 and Comparative Example 1, the addition of metal promoters to the catalysts in Examples 3-6 can greatly improve the catalytic reaction effect. The CO 2 conversion rate of the 0.04Cu-0.04KN-TDO / A catalyst reaches 34.74%, and the selectivity for the target product C 5 + hydrocarbon reaches 83.31%, and the selectivity for methane is only 9.36%.

[0065] 2) Compared with Comparative Example 1, oxalic acid was added during the preparation of the catalysts in Examples 1-2, which is beneficial to improving the effect of catalytic CO 2 conversion.

[0066] 3) Compared with Comparative Examples 2-3, in Example 1, ferric oxalate was directly loaded on alumina during the synthesis process, while in Comparative Examples 2-3, alumina was added after the synthesis of ferric oxalate (after the synthesis and drying of ferric oxalate). It can be seen from the XRD pattern that the diffraction peak of iron oxide in Example 1 is the weakest, indicating that its crystal grain size is the smallest and the iron oxide is more dispersed, which is beneficial to improving the effect of catalytic CO 2 conversion.

[0067] The content described in this specification is only a list of the implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as limited to the specific forms stated in the examples.

Claims

1. Application of a catalyst in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that the preparation method of the catalyst comprises the following steps: 1) Add soluble salts of metal M, alumina, oxalic acid dihydrate and an iron source into a mortar, mix evenly, and then grind until a yellow viscous substance or a powdery substance is formed to obtain a catalyst precursor; wherein, the iron source is one or more of ferric nitrate nonahydrate, iron acetylacetonate, and iron citrate; In step 1), the mass ratio of the alumina to the oxalic acid dihydrate is 1:0.05 - 0.6, and the mass ratio of the alumina to the Fe element in the iron source is 1:0.05 - 0.5; 2) After drying the catalyst precursor obtained in step 1), it is calcined in an air atmosphere at 300 - 600 °C for 1 - 6 h to obtain a catalyst doped with metal element M applicable to the production of higher carbon hydrocarbons by CO 2 hydrogenation; Metal M is Cu and K, and the soluble salt of metal M is its nitrate.

2. Application of a catalyst as described in claim 1 in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that In step 1), the mass ratio of the alumina to the oxalic acid dihydrate is 1:0.3 - 0.4; in step 1), the mass ratio of the alumina to the Fe element in the iron source is 1:0.1 - 0.

2.

3. Application of a catalyst as described in claim 1 in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that In step 2), the drying temperature is 50 - 120 °C and the time is 1 - 8 h.

4. Application of a catalyst as described in claim 1 in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that The mass of the doped metal element M is 1 - 20% of the mass of the alumina raw material.

5. Application of a catalyst as described in claim 4 in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that The mass of the doped metal element M is 9 - 15% of the mass of the alumina raw material.

6. Application of a catalyst as described in claim 1 in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that The catalytic reaction is carried out in a fixed-bed reactor. The catalyst is loaded in the isothermal section of the fixed-bed reactor, and H is introduced. 2 It is reduced at 300 - 500 °C for 4 - 12 h, and then the reaction temperature is adjusted to 260 - 400 °C, the reaction pressure is 1 - 7 MPa, and the reaction volume space velocity is 1500 - 8000 h -1 , H 2 / CO 2 The molar ratio is 2 - 3:1, and hydrogenation of carbon dioxide to produce higher hydrocarbons is carried out.

7. Application of a catalyst as described in claim 6 in hydrogenating carbon dioxide to produce higher carbon hydrocarbons, characterized in that The higher carbon hydrocarbons are hydrocarbon substances with no less than 5 carbon atoms.

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