Preparation method and application of high-stability plasma enhanced reforming catalyst

Abstract

The invention discloses a preparation method and application of a high-stability plasma enhanced reforming catalyst, particularly relates to a catalyst for converting two main greenhouse gases, namely CO2 and CH4, into synthesis gases (CO and H2), and belongs to the fields of waste gas treatment technologies and environment-friendly catalytic environments. The preparation method comprises the following steps: firstly, adding metered Ni (NO3) 2.6 H2O and Nd (NO3) 2.6 H2O (the mass percent of active components Ni in the catalyst is 10% and the mass percent of Nd is 5%) into a beaker, and adding a proper amount of deionized water to dissolve the components to obtain a transparent solution; adding the weighed and metered MCM-41 molecular sieve carrier into the obtained transparent solution, uniformly stirring to obtain mixed slurry, and dipping for 45 minutes; drying in a water bath in a constant-temperature heating magnetic stirrer at 80 DEG C, taking out, and drying in a drying oven at 110 DEG C for 12 hours; and activating by using radio frequency plasma (the discharge power is 200W, the treatment atmosphere is ethanol, and the activation time is 1h) to obtain the Nd modified Ni-Nd / M-P (EA) catalyst. The Ni-Nd / M-P (EA) catalyst prepared by the method has excellent catalytic activity and stability, and the preparation method is easy to operate, short in time consumption and low in cost.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a high-stability plasma-enhanced reforming catalyst, which is a catalyst that simultaneously utilizes two main greenhouse gases, CO 2 and CH 4 Converted into synthesis gas (CO and H 2 ) catalyst, which belongs to the field of waste gas treatment technology and environmental catalysis. Background Art

[0002] As a large amount of greenhouse gas CO 2 The emission of CO2 has caused global warming and serious environmental problems. In addition, burning fossil fuels is unsustainable due to limited resources. Therefore, storing or recycling CO2 is a 2 Used to produce fuels or chemicals, it is possible to achieve CO 2 The emission reduction target may also produce chemicals that can replace fossil fuels, which can not only reduce greenhouse gas emissions but also alleviate the energy crisis.

[0003] Methane dry reforming is currently the most promising CO 2 One of the technologies uses high temperatures (above 700°C) and catalysts to convert two greenhouse gases, CH 4 and CO 2 Producing synthesis gas (CO and H 2 ), which has bilateral advantages in mitigating global warming and providing valuable chemicals and fuels. Therefore, the development of methane dry reforming catalysts with high activity and stability is imperative.

[0004] The catalyst for the DRM reaction is mainly Ni-based catalyst. Ni is widely used because of its catalytic activity comparable to that of precious metals and its abundant reserves. However, Ni-based catalysts are prone to sintering and carbon deposition during high-temperature reactions, which causes the catalyst to deactivate rapidly. This is the biggest challenge in the industrialization of Ni-based catalysts for methane dry reforming. Therefore, how to improve the reforming stability and anti-carbon deposition performance of Ni-based catalysts is currently a hot topic in the field of methane dry reforming. Yuan et al. synthesized a Nd-doped nickel catalyst precursor using a coprecipitation method, and then calcined it in air at 800°C for 5h to obtain a series of hydrotalcite-derived NiNd x MgAlO catalyst. The results show that when the Nd doping amount is 7.5%, it has the smallest particle size (8.1nm) and the highest dispersion (11.8%), exposing more active sites. In addition, Nd doping reduces the apparent activation energy required for the reaction and significantly improves the catalytic activity. However, its stability is poor, and the preparation process is costly and complex, making it difficult to industrialize.

[0005] The design idea of ​​this patent is to prepare a supported Ni-based catalyst with highly dispersed active components, small particle size and strong metal-carrier interaction. The literature reports that the MCM-41 mesoporous molecular sieve with high specific surface area is used as a carrier, which can improve the dispersibility of the active component Ni and make the Ni-based catalyst have good activity and stability. However, the stability of the catalyst is poor. In addition, the literature also reports that the introduction of plasma during the preparation process can significantly enhance the metal-carrier interaction and reduce the Ni particle size. It is thought that the stronger metal-carrier interaction and the smaller Ni particle size can significantly improve the reforming performance of the catalyst, but the reality is that the catalyst has excellent stability and low catalytic activity. Therefore, based on the literature reports, we modified the catalyst by doping with metal additives (Ba, Sr, Nd, Sm) with better promotion performance, and found that the Nd-doped catalyst has better reforming performance, but overall the stability of the catalyst is still unsatisfactory. Summary of the invention

[0006] The purpose of the present invention is to develop a preparation method with low cost, simple preparation process, easy operation and excellent reforming performance. This patent introduces ethanol into Nd-doped supported Ni-based catalyst by radio frequency plasma, and studies the effect of the synergistic effect of Nd and ethanol plasma on the structure, reforming activity and stability of Ni-based catalyst. With Ni as the active component and MCM-41 as the carrier, the modified Ni-based catalyst is enhanced by doping the metal additive Nd and introducing ethanol by radio frequency plasma. Finally, the Ni-Nd / MP(EA) catalyst with the best reforming performance is obtained. Compared with the basic Ni / MC catalyst, the initial CH 4 The conversion rate was 82.51% (increased by 10.99%), and the initial CO 2 The conversion rate was 84.42% (increased by 13.14%), and the CO yield was 69.90% (increased by 9.93%). The 20h DRM stability test showed that after 20h of reaction, its CH 4 The conversion rate only dropped to 1.43%.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A method for preparing a metal-synergistic ethanol plasma-enhanced modified methane dry reforming catalyst comprises the following steps:

[0009] (1) Weigh the active component Ni(NO 3 ) 2 6H 2 O, additive Nd(NO 3 ) 2 6H 2O,n(Ni(NO 3 ) 2 6H 2 O):n(Nd(NO 3 ) 2 6H 2 O) = 10:5, add 30 ml of deionized water and stir until it is completely dissolved to obtain a transparent solution;

[0010] (2) adding a measured amount of MCM-41 molecular sieve carrier to the transparent solution obtained in step (1) to obtain a mixed slurry;

[0011] (3) soaking the mixed slurry obtained in step (2) for 45 minutes;

[0012] (4) adding a magnetic stirrer to the mixed slurry obtained in step (3), and rotating and stirring in a constant temperature heated magnetic stirrer until the mixture is evaporated to dryness to form a powder;

[0013] (5) placing the powder obtained in step (4) in an oven and drying overnight to obtain a green powder;

[0014] (6) The powder obtained in step (5) is placed in a muffle furnace, calcined, and naturally cooled to room temperature, or placed in a radio frequency plasma device for treatment, pressed into tablets, and ground into catalysts with a size of 20 to 40 mesh, thereby obtaining a catalyst for dry reforming of methane to produce synthesis gas.

[0015] According to the above scheme, the activation method is baking or radio frequency (RF) plasma.

[0016] According to the above scheme, the mass percentage of the carrier is 100%, and the mass percentage of the auxiliary agent Ce is 5%.

[0017] According to the above scheme, the treatment time of the RF plasma is 1h and the power is 200W.

[0018] According to the above scheme, the RF plasma treatment atmosphere is ethanol.

[0019] According to the above scheme, the mass percentage of the carrier is 100%, and the mass percentage of the active component Ni is 10%.

[0020] According to the above scheme, the carrier is MCM-41 molecular sieve.

[0021] According to the above scheme, the stirring temperature is 80°C;

[0022] Preferably, the drying temperature is 110°C;

[0023] The drying time is 12h;

[0024] The calcination temperature is 550°C;

[0025] The calcination time is 4 hours.

[0026] The present invention also provides the use of a methane dry reforming catalyst prepared by the preparation method described in any one of the above technical solutions in carbon dioxide conversion.

[0027] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0028] 1. The ethanol plasma enhanced impregnation method of the present invention is used to prepare the Nd-doped Ni-based catalyst for methane dry reforming reaction. The catalytic activity of the catalyst is significantly improved compared with the Ni-based catalyst prepared by impregnation. At 700°C, the initial conversion rates of methane and carbon dioxide reached 82.51% and 84.42%, respectively, which are significantly improved compared with the basic Ni / MC catalyst. The 20h stability evaluation shows that after reacting at 700°C for 20h, CH 4 The conversion rate was only reduced by 1.43%.

[0029] 2. Use ethanol plasma instead of traditional calcination to activate Ni-based catalysts in a green and efficient manner;

[0030] 3. Ni-Nd / MCM-41 molecular sieve catalyst was prepared by "impregnation + ethanol plasma treatment". This preparation method has low cost, simple preparation process, easy operation and high catalytic activity for methane dry reforming reaction. It can also be used for CO 2 Methanation and other reactions are suitable for industrial production.

[0031] Figure 1 The catalytic performance test chart of the catalysts prepared in Examples 1, 2, 3, 4 and 5.

[0032] Figure 2 The catalytic performance test chart of the catalysts prepared in Examples 1, 5, 6 and 7.

[0033] Figure 3 The XRD spectra of the catalysts prepared in Examples 1, 2, 3, 4 and 5 are shown.

[0034] Figure 4 The XRD spectra of the catalysts prepared in Examples 1, 5, 6 and 7 are shown.

[0035] Figure 5 H is the catalyst prepared in Example 1, Example 5, Example 6 and Example 7. 2 -TPR curve graph.

[0036] Figure 6 The XPS spectra of the catalysts prepared in Examples 1, 5, 6 and 7 are shown. DETAILED DESCRIPTION

[0037] The present invention will be further described below through some implementation examples, but the present invention is not limited thereto.

[0038] Example 1

[0039] The preparation steps for methane dry reforming catalyst are as follows:

[0040] Weigh 0.991 g of Ni(NO 3 ) 2 6H 2 O is placed in a beaker, 30 ml of deionized water is added to dissolve it, and then 1.8 g of MCM-41 molecular sieve is added. After being immersed at room temperature for 45 min, it is dried in a water bath in a constant temperature heated magnetic stirrer at 80 ° C, and then taken out and placed in a 110 ° C oven for drying for 12 h; it is placed in a muffle furnace and calcined at 550 ° C for 4 h in an air atmosphere, and the calcined powder is crushed into 20-40 meshes by a tablet press at a pressure of 8 Mp to obtain a Ni / MC catalyst.

[0041] Catalyst Evaluation

[0042] The stability evaluation of the catalyst was carried out in a self-made continuous flow fixed bed reactor. The reaction tube was a quartz tube with an inner diameter of 6 mm and a length of 33 cm. The reaction temperature was measured by a thermocouple placed in the middle of the reaction tube and controlled by a program temperature controller. The gas flow was controlled by a mass flow meter with an air velocity of 36000 ml / (h·g cat ), reaction raw gas: 24.0ml / min CH 4 , 27.7ml / min CO 2 In the experiment, the catalyst dosage was 0.1 g, the reaction temperature was 700 °C, and samples were taken every half an hour. The gas composition of the reactants and products was analyzed by a profile gas chromatograph (SC3000B) to calculate CH 4 and CO 2 The catalyst reacted with CH at different time points. 4 and CO 2 The conversion curve is as follows Figure 1 As shown, CH 4 and CO 2 The initial conversion rates are shown in Table 1.

[0043] Embodiment 2-5

[0044] Compared with Example 1, the difference is that metal additives are added. The added metal additives are Ba, Sr, Sm, and Nd, and the mass percentage of the additives is 5%. Specifically, 0.991g of Ni(NO 3 ) 2 6H 2O and corresponding dosage of auxiliary agent were placed in a beaker, and the other processes were the same as those in Example 1 to prepare Ni-X / MCM-41 catalyst. The catalyst compositions of Examples 2 to 5 are shown in Table 1.

[0045] Catalyst Evaluation

[0046] According to the evaluation method of Example 1, the catalyst reacted with CH 4 and CO 2 The conversion curve is as follows Figure 1 As shown, CH 4 and CO 2 The initial conversion rates are shown in Table 1.

[0047] Example 6

[0048] Compared with Example 1, the difference is the catalyst activation method, the specific activation method is the plasma method, and the other processes are the same as Example 1, and a Ni / MP (EA) catalyst is obtained. The catalyst composition of Example 6 is shown in Table 1.

[0049] Catalyst Evaluation

[0050] According to the evaluation method of Example 1, the catalyst reacted with CH 4 and CO 2 The conversion curve is as follows Figure 2 As shown, CH 4 and CO 2 The initial conversion rates are shown in Table 1.

[0051] Example 7

[0052] Compared with Example 1, the difference is that the metal additive is doped and the activation method is used. The other processes are the same as those in Example 1, which are as follows: 0.991 g of Ni(NO 3 ) 2 6H 2 O and Nd(NO 3 ) 2 6H 2 O in a beaker, add 30ml of deionized water to dissolve it, add 1.8g of MCM-41 molecular sieve, soak at room temperature for 45min, dry it in a water bath in a constant temperature heated magnetic stirrer at 80℃, then take it out and place it in a 110℃ oven to dry for 12h; gasify the ethanol with a plasma grafting instrument and pass it into the radio frequency plasma treatment area. At the same time, place the dried catalyst precursor in the plasma treatment area for activation for 1h, the plasma discharge power is 200W, and the treatment atmosphere is ethanol, that is, the Ni-Nd / MP (EA) catalyst is prepared. The catalyst composition of Example 7 is shown in Table 1.

[0053] Catalyst Evaluation

[0054] According to the evaluation method of Example 1, the catalyst reacted with CH 4 and CO 2 The conversion curve is as follows Figure 2 As shown, CH 4 and CO 2 The initial conversion rates are shown in Table 1.

[0055] Example Molecular sieve catalyst composition table:

[0056] Specific examples of molecular sieve catalyst processing parameters and activity evaluation are shown in Table 1:

[0057] Stability Evaluation of Molecular Sieve Catalysts

[0058] The catalytic performance of the catalyst was evaluated in a self-made continuous flow fixed bed reactor. The reaction tube was a quartz tube with an inner diameter of 6 mm and a length of 33 cm. The reaction temperature was measured by a thermocouple placed in the middle of the reaction tube and controlled by a program temperature controller. The gas flow was controlled by a mass flow meter with an air velocity of 36000 ml / (h·g cat ), reaction raw gas: 24.0ml / min CH 4 , 27.7ml / min CO 2 In the experiment, the catalyst dosage was 0.1 g, the reaction temperature was 700°C, and samples were taken every half an hour for a total of 20 hours. The gas composition of the reactants and products was analyzed by a profile gas chromatograph (SC3000B). The catalytic performance curves of the catalysts prepared in Examples 1, 2, 3, 4, 5, 6 and 7 at different time points are shown in the figure below: Figure 1 and Figure 2 shown.

[0059] The specific catalyst stability evaluation results are shown in Table 2:

[0060] XRD characterization

[0061] The XRD spectrum of the metal-doped catalyst before the reaction is as follows: Figure 3 All catalysts have a peak at 2θ = 22°, which is amorphous SiO 2 Characteristic diffraction peaks, and NiO characteristic diffraction peaks appear at 2θ = 37.2°, 43.3°, 62.9°, 75.4° and 79.4° [PDF#47-1049]. However, compared with the conventional Ni / MC catalyst, the intensity of its Ni characteristic diffraction peaks is significantly reduced after doping with metal additives, indicating that doping with metal additives can improve the dispersion of Ni particles on the support surface to a certain extent, thereby reducing the Ni particle size of the catalyst.

[0062] Figure 4 XRD spectra of catalysts activated by ethanol plasma. In the figure, strong NiO characteristic diffraction peaks are observed at 2θ=37.2°, 43.3°, 62.9°, 75.4° and 79.4°[PDF#47-1049] for Ni / MC and Ni-Nd / MC catalysts activated by conventional calcination. However, the NiO characteristic diffraction peaks are almost invisible for the catalyst activated by ethanol plasma, which indicates that ethanol plasma treatment can significantly improve the dispersion of NiO particles, making NiO highly dispersed on the surface of MCM-41 carrier or in amorphous form, reducing the crystallinity of the catalyst, thereby reducing the particle size of the active component.

[0063] H 2 -TPR Characterization

[0064] Figure 5 H is the catalyst activated by ethanol plasma 2 -TPR curve. In the figure, the high-temperature reduction peaks of all catalysts move upward, indicating that both metal doping and ethanol plasma activation can enhance the metal-support interaction of the catalyst and improve the stability of the catalyst. Surprisingly, the low-temperature reduction peak of the catalyst activated by ethanol plasma moves lower, indicating that the catalyst activated by ethanol plasma has easily reducible Ni species and the Nd-doped catalyst has a strong metal-support interaction. This means that the synergistic effect of Nd and ethanol plasma can make the catalyst have excellent stability while improving its activity.

[0065] XPS characterization

[0067] In order to observe the synergistic effect of Nd and ethanol plasma on the valence state of Ni-based catalysts, XPS characterization tests were performed on fresh catalysts. The results are shown in Figure 6 As shown. Figure 6 As can be seen from (a), whether it is metal doping or ethanol plasma activation, the Ni binding energy can move upward. Among them, the catalyst activated by Nd and ethanol plasma has the highest binding energy, which indicates that the combined action of the two can significantly enhance the metal-support interaction of the catalyst, and the Ni species that are easy to reduce are mostly, which is consistent with the H 2 -TPR characterization results are consistent. In addition, Figure 6 As can be seen in (b), the catalyst has a higher adsorbed oxygen content, which indicates that hydroxyl groups have been successfully introduced, which is beneficial to reduce carbon deposition and thus improve the stability of the catalyst.

Claims

1. A preparation method and application of a high-stability plasma-enhanced reforming catalyst, characterized in that: The method comprises the following steps: (1) Weigh the active component Ni(NO3)2·6H2O and the auxiliary agent Nd(NO3)2·6H2O in a stoichiometric ratio of n(Ni(NO3)2·6H2O):n(Nd(NO3)2·6H2O)=10:5, add 30 ml of deionized water, and stir until completely dissolved to obtain a transparent solution; (2) adding a measured amount of MCM-41 molecular sieve carrier to the transparent solution obtained in step (1) to obtain a mixed slurry; (3) soaking the mixed slurry obtained in step (2) for 45 minutes; (4) adding a magnetic stirrer to the mixed slurry obtained in step (3), and rotating and stirring in a constant temperature heated magnetic stirrer until the mixture is evaporated to dryness to form a powder; (5) placing the powder obtained in step (4) in an oven and drying overnight to obtain a green powder; (6) The powder obtained in step (5) is placed in a muffle furnace, calcined, and naturally cooled to room temperature, or placed in a radio frequency plasma device for treatment, pressed into tablets, and ground into catalysts with a size of 20 to 40 mesh, thereby obtaining a methane dry reforming catalyst.

2. The method for preparing a high-stability plasma-enhanced reforming catalyst according to claim 1, characterized in that: The activation method is baking or radio frequency (RF) plasma.

3. The method for preparing a high-stability plasma-enhanced reforming catalyst according to claim 1-2, characterized in that: The treatment time of the radio frequency plasma is 1 hour, and the power is 200W.

4. The method for preparing a high-stability plasma-enhanced reforming catalyst according to any one of claims 1 to 3, characterized in that: The carrier is MCM-41 molecular sieve.

5. The method for preparing a high-stability plasma-enhanced reforming catalyst according to any one of claims 1 to 4, characterized in that: The mass percentage of the carrier is 100%, and the mass percentage of the active component Ni is 10%.

6. The method for preparing a high-stability plasma-enhanced reforming catalyst according to any one of claims 1 to 5, characterized in that: Taking the mass of the carrier as 100%, the mass percentage of the auxiliary agent Ce is 5%.

7. The method for preparing a high-stability plasma-enhanced reforming catalyst according to any one of claims 1 to 6, characterized in that: The plasma treatment atmosphere was ethanol.

8. The method for preparing a high-stability plasma-enhanced reforming catalyst according to any one of claims 1 to 7, characterized in that: The stirring temperature is 80° C.; the drying temperature is 110° C.; and the drying time is 12 hours.

9. The high stability plasma enhanced reforming catalyst according to any one of claims 1 to 8 is used for carbon dioxide conversion.

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