A carbon-supported nanoscale gadolinium-cobalt catalyst, its preparation method and use

Abstract

The application relates to a carbon-loaded nanoscale gadolinium-cobalt catalyst and a preparation method and application thereof, and relates to the technical field of catalysts for CO2 hydrogenation reactions. The application solves the problems of easy agglomeration, large hydrogen consumption and poor catalytic performance of existing catalysts for CO2 hydrogenation to prepare methane. Activated carbon is acid-treated and degassed; cobalt nitrate, gadolinium nitrate and tea leaf extract are mixed with the acid-treated activated carbon, NH4OH is added dropwise until the pH is 8-8.5, and oil bath stirring is performed for co-precipitation; the co-precipitation product is washed and dried; and calcination treatment is performed under an inert atmosphere; and reduction treatment is performed by using H2. The catalyst provided by the application can be applied to CO2 catalytic hydrogenation reactions, and not only improves the catalytic performance, but also saves hydrogen energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of methanation catalysts, in particular to a carbon-supported nanoscale gadolinium-cobalt catalyst, a preparation method and application thereof. BACKGROUND

[0002] CO2 hydrogenation to produce methane (i.e. methanation reaction) has attracted extensive attention due to its carbon recycling and methane as a clean fuel or chemical raw material. Methane, as a low-carbon energy source with high energy density, has a combustion heat of 890 kJ / mol, which can be directly used for heating, industrial heating, and other scenarios. It can also be used as a core component of natural gas, which can be connected to the existing natural gas pipeline without large-scale infrastructure modification. At the same time, it can also be used as a chemical raw material to synthesize methanol, dimethyl ether and other high-value-added products, which has irreplaceable application value in energy supply and chemical production. The core of this reaction is the development of high-efficiency catalysts, which need to have high activity, high selectivity, good stability and excellent metal dispersion to ensure efficient conversion of CO2 and high yield of methane under mild conditions, and to avoid the generation of by-products, which reduces the purity of methane and affects its application value in energy or chemical industry.

[0003] Currently, the catalysts for CO2 hydrogenation to produce methane mostly use transition metals as active components and rare earth metals as additives. However, there are still many technical bottlenecks in the preparation process of the catalysts. On the one hand, metal ions are prone to agglomeration during the precipitation process, which reduces the metal dispersion and affects the number of active sites and the catalytic efficiency of the catalyst. On the other hand, a large amount of hydrogen H2 is often needed for subsequent reduction in traditional preparation methods, which not only increases the preparation cost and energy consumption, but also may cause the metal particles to grow due to excessive reduction, further weakening the performance of the catalyst.

[0004] To solve the problem of metal agglomeration, the existing technology mostly uses the addition of surfactants or complexing agents to regulate the metal dispersion. However, the introduction of such substances may remain in the catalyst, which has a negative impact on the catalytic reaction, and the subsequent separation and treatment steps are complicated, which is not conducive to industrial production. In addition, the optimization of the ratio of rare earth metal additives to transition metal active components and the calcination and reduction process parameters are still key difficulties to improve the selectivity and stability of the catalyst, and the existing solutions have not formed a mature preparation system that takes into account performance, cost and environmental requirements.

[0005] Therefore, it is of great significance to develop a catalyst that can effectively regulate metal dispersion, reduce the amount of H2, has a simple process and excellent catalytic performance, which can promote the industrial application of CO2 hydrogenation to produce methane. SUMMARY

[0006] In order to solve the above problems existing in the prior art, the application provides a carbon-loaded nanoscale gadolinium-cobalt catalyst and a preparation method and application thereof.

[0007] The technical scheme of the application is as follows:

[0008] The preparation method of the carbon-loaded nanoscale gadolinium-cobalt catalyst comprises the following steps:

[0009] S1, acidizing treatment of activated carbon and degassing;

[0010] S2, mixing of cobalt nitrate, gadolinium nitrate and tea leaf extract solution with the acidized activated carbon, dropwise addition of NH4OH to pH 8-8.5, oil bath stirring and co-precipitation;

[0011] S3, washing and drying of the co-precipitation product;

[0012] S4, calcination treatment under an inert atmosphere;

[0013] S5, reduction treatment with H2.

[0014] Preferably, the step S1 specifically comprises:

[0015] The activated carbon is added into a strong acid solution at a solid-liquid ratio of 1g:5-10mL, continuous stirring is performed, heating reflux treatment is carried out under the condition of a 60-80 DEG C water bath, the reflux time is 2-4h, after the system is cooled to room temperature, the mixed solution is subjected to suction filtration separation, the filter cake-shaped activated carbon is collected, washed with deionized water until the washing liquid pH is 6.5-7.0, and after complete drying, the activated carbon is transferred to a vacuum tube furnace, heated to 150-200 DEG C at a rate of 5-10 DEG C / min under the condition of a vacuum degree not less than 0.09MPa, and kept for 1-2h.

[0016] Preferably, the strong acid solution is hydrochloric acid or nitric acid with a concentration of 3-6mol / L.

[0017] Preferably, the tea leaf extract solution is prepared by the following steps:

[0018] The tea leaves are crushed to a particle size of less than 1mm, a mass-volume ratio of 1g / 10mL is used, a 80 DEG C water bath is used for extraction for 15min, then cooled to 40 DEG C, 1.5wt% cellulase, 1.5wt% tannase and 1.1wt% protease are added, enzyme hydrolysis is carried out for 2-3h, then enzyme inactivation is carried out at 100 DEG C for 5min, then cooled to room temperature, and finally filtered to obtain the extract solution.

[0019] Preferably, the mixing ratio of the cobalt nitrate, gadolinium nitrate, tea leaf extract solution and acidized activated carbon in the step S2 is 4.41-4.43g:0.28-0.3g:2750-3300mL:10g.

[0020] Preferably, the drying temperature in step S3 is 80 DEG C, and the drying time is 12h.

[0021] Preferably, the calcination treatment in step S4 is specifically: calcination at 300 DEG C for 1h under nitrogen, and then calcination at 500 DEG C for 1h.

[0022] Preferably, the H2 reduction temperature is 350 DEG C, and the reduction time is 0.5-2h.

[0023] The application further provides a carbon-loaded nanoscale gadolinium-cobalt catalyst prepared by the preparation method.

[0024] The application further provides an application of the carbon-loaded nanoscale gadolinium-cobalt catalyst, and the application is specifically applied to catalyzing a carbon dioxide hydrogenation reaction to prepare methane.

[0025] Compared with the prior art, the application has the following specific beneficial effects:

[0026] The acidification and degassing of the activated carbon can effectively increase the surface active sites thereof, and create good conditions for subsequent active component loading; during the preparation of the tea leaf extract, specific enzymatic treatment can release polyphenols such as catechins, and these substances can inhibit catalyst particle agglomeration, optimize the microstructure, and improve the dispersion of the active component in the subsequent step; on the other hand, the hydrogen consumption during the subsequent reduction treatment can be reduced by virtue of the reducing property of the substances, and hydrogen resources can be saved.

[0027] By reasonably regulating the gadolinium-cobalt ratio and the reduction temperature, when the gadolinium-cobalt ratio is 1:9 and the reduction temperature is 350 DEG C, a phase more conducive to the carbon dioxide hydrogenation reaction can be formed, the catalyst exhibits excellent catalytic performance, the catalytic effect on the carbon dioxide hydrogenation to prepare methane is further improved, the carbon dioxide conversion rate and the methane selectivity are both at a high level, and the application has a significant advantage in the resource utilization of carbon dioxide. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 FIG. 1 is a scanning electron microscope (SEM) image of a catalyst sample in Example 1;

[0029] Figure 2 FIG. 3 is an SEM image of a catalyst sample in Comparative Example 3;

[0030] Figure 3 FIG. 5 is an XRD spectrum of the catalyst samples obtained in the examples;

[0031] Figure 4 FIG. 7 is a schematic diagram of a comparison of the catalytic effects of the catalyst samples obtained in the examples;

[0032] Figure 5Catalytic data of Gd1Co9-350-T at different reduction temperatures

[0033] Figure 6 Catalytic data of Gd1Co9-350 at different reduction temperatures

[0034] Figure 7 Catalytic data of Co-350-T at different reduction temperatures

[0035] Figure 8 Catalytic data of Gd-350-T at different reduction temperatures

[0036] Figure 9 Catalytic data comparison diagram of Example 1 and Comparative Example 4. DETAILED DESCRIPTION

[0037] In order to make the technical solutions of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the specification of the present application. It should be noted that the following embodiments are only used to better understand the technical solutions of the present application, and should not be understood as a limitation of the present application.

[0038] Example 1.

[0039] (1) Take 10 g of activated carbon with a particle size of 20-100 mesh, and add 6 mol / L nitric acid solution according to a solid-liquid ratio of 1 g:8 mL. Stir at a speed of 250 r / min, heat in a constant temperature water bath at 70°C for 3 h, and then cool to room temperature. After the reaction is completed, separate the activated carbon by suction filtration, and wash repeatedly with deionized water until the pH of the washing liquid is 6.8. Dry the washed activated carbon in a 90°C air-drying oven for 5 h, and then transfer it to a vacuum tube furnace. Under the condition of a vacuum degree of 0.1 MPa, heat it to 180°C at a rate of 8°C / min, and keep it at this temperature for 1.5 h to complete degassing. After cooling, it is ready for use.

[0040] (2) Select green tea leaves, crush them, and pass them through an 18-mesh sieve. Take 100 g of tea powder and add it to 1000 mL of deionized water according to a ratio of 1 g:10 mL. After 15 min of extraction in a 80°C water bath, immediately cool it in a cold water bath to 40°C. Add cellulase (5000 U / g) at a concentration of 1.5 wt%, tannase (3000 U / g) at a concentration of 1.5 wt%, and protease (2000 U / g) at a concentration of 1.1 wt%, and carry out enzymatic hydrolysis at 40°C for 2.5 h. After the enzymatic hydrolysis is completed, heat it to 100°C for 5 min to inactivate the enzymes. After cooling to room temperature, vacuum suction filter it through a 0.22 μm filter membrane to obtain the tea extract.

[0041] (3) Put 10 g of treated activated carbon into a 5 L three-necked flask, and then add 4.42 g of cobalt nitrate (Co(NO3)2·6H2O), 0.29 g of gadolinium nitrate (Gd(NO3)3·6H2O) and 3000 mL of the tea leaf extract prepared in step 2, and mix at a stirring rate of 300 r / min for 30 min. Then, add 1.5 mol / L of NH4OH solution at a rate of 1 drop / s, and stop the addition when the pH value is monitored to be 8.2, and continue to stir in an 80°C oil bath for 2 h to complete the co-precipitation.

[0042] (4) Separate the co-precipitation product by suction filtration, wash it with deionized water for 3 times, collect the filter cake and dry it in a 80°C air-drying oven for 12 h to obtain black precursor powder.

[0043] (5) Transfer the dried precursor powder to a porcelain boat, and place it in a tube furnace, and first heat it to 300°C at a rate of 5°C / min under a nitrogen atmosphere, and then heat it to 500°C at a rate of 5°C / min under a nitrogen atmosphere, and then naturally cool it to room temperature.

[0044] (6) Place the calcined product in a reduction furnace, and heat it to 350°C at a rate of 10°C / min under a pure hydrogen atmosphere (flow rate: 30 mL / min), and keep it at 350°C for 1 h for reduction treatment, and then cool it to room temperature under a nitrogen atmosphere to obtain a carbon-supported nanoscale gadolinium-cobalt catalyst, which is recorded as Gd1Co9-350-T.

[0045] Example 2.

[0046] (1) and (2) are the same as the operations in Example 1.

[0047] (3) Put 10 g of treated activated carbon into a 5 L three-necked flask, and then add 3.93 g of cobalt nitrate (Co(NO3)2·6H2O), 0.58 g of gadolinium nitrate (Gd(NO3)3·6H2O) and 3000 mL of the tea leaf extract prepared in step 2, and mix at a stirring rate of 300 r / min for 30 min. Then, add 1.5 mol / L of NH4OH solution at a rate of 1 drop / s, and stop the addition when the pH value is monitored to be 8.3, and continue to stir in an 80°C oil bath for 2 h to complete the co-precipitation.

[0048] (4), (5) and (6) are the same as Example 1, and a carbon-supported nanoscale gadolinium-cobalt catalyst is obtained, which is recorded as Gd2Co8-350-T.

[0049] Example 3.

[0050] (1) and (2) are the same as the operations in Example 1.

[0051] (3) 10 g of the treated activated carbon was added into a 5 L three-necked flask, and 2.95 g of cobalt nitrate (Co(NO3)2·6H2O), 1.16 g of gadolinium nitrate (Gd(NO3)3·6H2O) and 3000 mL of tea leaf extract solution were sequentially added, and mixed at a stirring rate of 300 r / min for 30 min. Then, 1.5 mol / L of NH4OH solution was added dropwise at a rate of 1 drop / s, and the pH value was monitored in real time until it reached 8.2, at which point the dropwise addition was stopped, and the stirring was continued in an 80°C oil bath for 2 h to complete the coprecipitation.

[0052] (4), (5), (6) were the same as in Example 1, and a carbon-supported nanoscale gadolinium-cobalt catalyst was obtained, which was denoted as Gd4Co6-350-T.

[0053] Example 4.

[0054] (1)-(5) were the same as in Example 1.

[0055] (6) The calcined product was placed in a reduction furnace, and was heated to 500°C at a rate of 10°C / min under a pure hydrogen atmosphere (flow rate 30 mL / min), and was kept at this temperature for 1 h for reduction treatment. After the reduction was completed, the product was cooled to room temperature under nitrogen protection, and a carbon-supported nanoscale gadolinium-cobalt catalyst was obtained, which was denoted as Gd1Co9-500-T.

[0056] Example 5.

[0057] (1)-(5) were the same as in Example 2.

[0058] (6) was the same as in Example 4, and the catalyst obtained was denoted as Gd2Co8-500-T.

[0059] Example 6.

[0060] (1)-(5) were the same as in Example 3.

[0061] (6) was the same as in Example 4, and the catalyst obtained was denoted as Gd4Co6-500-T.

[0062] Example 7.

[0063] (1)-(5) were the same as in Example 1.

[0064] (6) The calcined product was placed in a reduction furnace, and was heated to 650°C at a rate of 10°C / min under a pure hydrogen atmosphere (flow rate 30 mL / min), and was kept at this temperature for 1 h for reduction treatment. After the reduction was completed, the product was cooled to room temperature under nitrogen protection, and a carbon-supported nanoscale gadolinium-cobalt catalyst was obtained, which was denoted as Gd1Co9-650-T.

[0065] Example 8.

[0066] (1)-(5) were the same as in Example 2.

[0067] (6) The same as example 7, the catalyst is recorded as Gd2Co8-650-T.

[0068] Example 9.

[0069] (1) - (5) The same as example 3.

[0070] (6) The same as example 8, the catalyst is recorded as Gd4Co6-650-T.

[0071] Comparative example 1.

[0072] (1) - (2) The same as example 1.

[0073] (3) 10 g of activated carbon after treatment was added to a 5 L three-necked flask, 4.91 g of cobalt nitrate (Co (NO3) 2·6H2O, corresponding to pure Co 1 g) and 3000 mL of tea leaf extract were added, and mixed at a stirring rate of 300 r / min for 30 min. 1.5 mol / L NH4OH was added dropwise to pH = 8.2, and stirred at 80°C oil bath for 2 h. 2+ 1g) and 3000 mL of tea leaf extract were added, and mixed at a stirring rate of 300 r / min for 30 min. 1.5 mol / L NH4OH was added dropwise to pH = 8.2, and stirred at 80°C oil bath for 2 h.

[0074] (4) - (6) The same as example 1, a pure cobalt catalyst was obtained, recorded as Co-350-T.

[0075] Comparative example 2.

[0076] (1) - (2) The same as example 1.

[0077] (3) 10 g of activated carbon after treatment was added to a 5 L three-necked flask, 2.90 g of gadolinium nitrate (Gd (NO3) 3·6H2O, corresponding to pure Gd 1 g) and 3000 mL of tea leaf extract were added, and mixed at a stirring rate of 300 r / min for 30 min. 1.5 mol / L NH4OH was added dropwise to pH = 8.2, and stirred at 80°C oil bath for 2 h. 3+ 1g) and 3000 mL of tea leaf extract were added, and mixed at a stirring rate of 300 r / min for 30 min. 1.5 mol / L NH4OH was added dropwise to pH = 8.2, and stirred at 80°C oil bath for 2 h.

[0078] (4) - (6) The same as example 1, a pure gadolinium catalyst was obtained, recorded as Gd-350-T.

[0079] Comparative example 3.

[0080] (1) The same as example 1.

[0081] (2) No tea leaf extract preparation process.

[0082] (3) Put 10 g of the treated activated carbon into a 5 L three-necked flask, and then add 4.42 g of cobalt nitrate, 0.29 g of gadolinium nitrate and 3000 mL of deionized water, and mix at a stirring rate of 300 r / min for 30 min. Add 1.5 mol / L NH4OH dropwise until the pH is 8.2, and then stir and react at 80°C in an oil bath for 2 h.

[0083] (4)-(6) are the same as in Example 1, to obtain a catalyst denoted as Gd1Co9-350.

[0084] Comparative Example 4.

[0085] (1)-(5) are the same as in Example 1.

[0086] (6) Put the calcined product into a reduction furnace, and then heat it to 350°C at a rate of 10°C / min in a pure hydrogen atmosphere (flow rate of 10 mL / min), and keep it at this temperature for 1 h to perform reduction treatment. After the reduction is completed, cool it to room temperature under nitrogen protection to obtain a carbon-supported nanoscale gadolinium-cobalt catalyst denoted as Gd1Co9-350-T-low hydrogen.

[0087] Effect Example 1.

[0088] Take the catalyst samples of Example 1 and Comparative Example 3 respectively, and place them under a scanning electron microscope to observe the microstructure characteristics such as sample morphology, particle size and distribution, as shown in Figure 1 and Figure 2 .

[0089] As can be clearly seen from the figures, the Gd1Co9-350-T catalyst of Example 1 has regular particle morphology, uniform size and good dispersibility, which is due to the action of the tea extract, which contains active ingredients that can effectively inhibit particle agglomeration, so that the catalyst has a good microstructure, which is conducive to the catalytic reaction. In Comparative Example 3, the particle agglomeration of the Gd1Co9-350 catalyst is obvious, and the morphology is irregular. This proves that the tea extract plays a key role in inhibiting the agglomeration of catalyst particles, and the absence of the tea extract will lead to a poor microstructure of the catalyst.

[0090] Effect Example 2.

[0091] The catalyst samples obtained in each example are tested by an X-ray diffractometer, and the results are shown in Figure 3 . By comparing the XRD spectra of the hydrogen-reduced samples with different Gd / Co ratios, it can be observed that the phase composition of the catalysts is different with the change of the Gd / Co ratio and the reduction temperature.

[0092] Figure 4The catalytic effect of the catalyst samples obtained in each embodiment in the process of preparing methane in the catalytic carbon dioxide hydrogenation reaction is shown in the schematic diagram. It can be seen that the CO2 conversion rate and CH4 selectivity of Gd1Co9 at a ratio of 350℃ reduction temperature are higher than those of other ratios and reduction temperatures. It may be due to the formation of a more favorable phase for CO2 hydrogenation reaction, such as metallic cobalt or cobalt and gadolinium alloy phase, which is the active center of catalytic reaction, at a ratio of Gd1Co9 and 350℃ reduction temperature.

[0093] Effect Example 3.

[0094] Figure 5 Gd1Co9-350-T catalytic data, Figure 6 Gd1Co9-350 catalytic data. By comparing the two sets of data, it can be seen that the CO2 conversion rate and CH4 selectivity of Gd1Co9-350-T are higher than those of Gd1Co9-350, which again proves that the tea extract can improve the catalytic performance by improving the microstructure of the catalyst and the dispersion of the active components.

[0095] Effect Example 4.

[0096] Figure 7 Co-350-T catalytic data, Figure 8 Gd-350-T catalytic data. It can be seen that Co-350-T has certain activity for CO2 hydrogenation to CH4, but Gd-350-T has very low activity, which shows that cobalt alone is the main active component, and gadolinium mainly plays an auxiliary role. Only when cobalt and gadolinium work together can they better catalyze CO2 hydrogenation to CH4.

[0097] Effect Example 5.

[0098] Figure 9 The catalytic data of Example 1 and Comparative Example 4 are compared in the schematic diagram.

[0099] It can be seen that the CO2 conversion rate and CH4 selectivity after reducing the amount of H2 are comparable to those under normal H2 usage, and are higher than those of Gd1Co9-350. This shows that the tea extract plays a certain reduction role in the preparation process, so that the amount of H2 can be reduced during subsequent reduction treatment, while the high activity and high selectivity of the catalyst can be ensured, thereby saving hydrogen resources.

[0100] Obviously, the above embodiments are only examples for the sake of clarity, and are not limiting of the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A process for the preparation of carbon supported nanosized gadolinium cobalt catalyst, characterized by, The preparation method comprises the following steps: S1, acidizing treatment of activated carbon, degassing; S2, mixing cobalt nitrate, gadolinium nitrate and tea leaf extract with the acidized activated carbon, adding NH4OH dropwise until the pH value is 8-8.5, and stirring and co-precipitating in an oil bath; S3, washing and drying the co-precipitated product; S4, calcination treatment under an inert atmosphere; S5, reduction treatment with H2; The tea leaf extract is prepared by the following steps: The tea leaves are crushed to a particle size of less than 1 mm, and then extracted in a water bath at 80 DEG C for 15 min at a mass / volume ratio of 1 g / 10 mL, and then cooled to 40 DEG C, and then 1.5 wt% cellulase, 1.5 wt% tannase and 1.1 wt% protease are added, and then enzymolysis is carried out for 2-3 h, and then the enzyme is inactivated at 100 DEG C for 5 min, and then cooled to room temperature, and finally filtered to obtain the extract; In step S2, the mixing ratio of the cobalt nitrate, gadolinium nitrate and tea leaf extract to the acidized activated carbon is 4.41-4.43 g:0.28-0.3 g:2750-3300 mL:10 g.

2. The process for the preparation of carbon supported nanosized gadolinium cobalt catalyst as claimed in claim 1 wherein, Step S1 specifically comprises: The activated carbon is added to a strong acid solution at a solid-liquid ratio of 1 g:5-10 mL, continuously stirred, heated and refluxed under the condition of a water bath at 60-80 DEG C, the refluxing time is 2-4 h, after the system is cooled to room temperature, the mixture is subjected to suction filtration separation, the filter cake-shaped activated carbon is collected, washed with deionized water until the pH value of the washing liquid is 6.5-7.0, and then completely dried, and then the activated carbon is transferred to a vacuum tube furnace, heated to 150-200 DEG C at a rate of 5-10 DEG C / min under the condition of a vacuum degree of not less than 0.09 MPa, and then kept for 1-2 h.

3. The process for the preparation of carbon supported nanosized gadolinium cobalt catalyst as claimed in claim 2, wherein, The strong acid solution is hydrochloric acid or nitric acid with a concentration of 3-6 mol / L.

4. The method of claim 1, wherein the carbon supported nanosized gadolinium cobalt catalyst is prepared by the steps of: In step S3, the drying temperature is 80 DEG C, and the drying time is 12 h.

5. The method of claim 1, wherein the carbon supported nanosized gadolinium cobalt catalyst is prepared by the steps of: In step S4, the calcination treatment specifically comprises: calcination at 300 DEG C for 1 h under the condition of nitrogen, and then calcination at 500 DEG C for 1 h.

6. The method of claim 1, wherein the carbon supported nanosized gadolinium cobalt catalyst is prepared by the steps of: The H2 reduction temperature is 350 DEG C, and the reduction time is 0.5-2 h.

7. A carbon-supported nanoscale gadolinium-cobalt catalyst prepared by the preparation method in any one of claims 1-6.

8. Use of a carbon supported nanosized gadolinium cobalt catalyst as claimed in claim 7, characterized in that, Applied to catalytic carbon dioxide hydrogenation reaction to prepare methane.

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