Method for preparing nickel-based bimetallic catalyst based on ball milling method

Abstract

The invention discloses a method for preparing a nickel-based bimetallic catalyst based on a ball-milling method, and belongs to the technical field of catalysis, the nickel-based bimetallic catalyst is prepared by adopting the ball-milling method, and a reaction for preparing methane through carbon dioxide hydrogenation driven by plasmas under a low-temperature condition is realized. The preparation process of the catalyst comprises the following steps: preparing a nickel-based bimetallic catalyst by adopting a dry ball milling method, taking acetylacetone metal salt and nano cerium oxide as raw materials, adding the raw materials and grinding beads into a ball milling tank, performing ball milling by using a planetary ball mill with set rotating speed and time, and calcining precursor powder obtained by ball milling to obtain the nickel-based bimetallic catalyst. And screening and performing high-temperature hydrogen reduction to obtain the nickel-based bimetallic catalyst. The catalyst has low-load and high-dispersion alloy active sites, relatively good carbon dioxide adsorption capacity and hydrogenation performance, and relatively high reaction activity under a low-temperature plasma condition, so that the conversion rate of carbon dioxide and the yield of methane are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysis, and in particular relates to a method for preparing a nickel-based bimetallic catalyst based on a ball milling method. Background Art

[0002] At present, as the main greenhouse gas in the atmosphere, the increase in CO2 concentration has caused a series of changes in the ecosystem, such as the destruction of the ozone layer and the melting of glaciers. Therefore, it is urgent to carry out research on CO2 emission reduction and its resource utilization. The main way to reduce carbon emissions in industry is to convert CO2 into high value-added products. Common high value-added products include methane and methanol, among which methane as fuel can largely meet energy needs. In the greenhouse, the CO2 methanation reaction is spontaneous and is a strong exothermic reaction. Lower temperatures are conducive to the reaction. Therefore, it is of great significance to develop low-temperature and high-efficiency catalysts and realize the CO2 methanation reaction under mild conditions.

[0003] Low-temperature plasma catalysis technology is considered to be a unique technology for achieving CO2 methanation under ambient conditions. The technology has unique advantages such as relatively mild conditions and simple reaction equipment. Low-temperature plasma catalytic CO2 methanation provides very fast activation and conversion of CO2 under ambient conditions. The catalytic performance is superior to traditional thermal catalysis, and it can flexibly and conveniently store renewable electricity and convert CO2 into high value-added products.

[0004] Studies have shown that the properties of metal centers and catalyst carriers (e.g., metal dispersion, size, and structure) play a key role in promoting plasma-catalyzed CO2 methanation. Many active metals (e.g., Ru, Ni, Cu, Co, etc.) have been used in CO2 hydrogenation catalytic reactions, among which nickel is widely used due to its low cost and good activity. The morphology, pore structure, dielectric properties, and surface alkalinity of the carrier are also very important for the performance of plasma-catalyzed CO2 methanation. These properties will affect the plasma microdischarge and CO2 adsorption capacity, thereby dominating the performance of low-temperature plasma-catalyzed CO2 methanation. CeO2, as a carrier of nickel-based catalysts, has abundant surface oxygen vacancies and strong alkalinity, which can effectively improve CO2 adsorption and dielectric constant, thereby effectively improving the CO2 conversion rate.

[0005] Here, we propose a dry ball milling method to effectively synthesize Ni-based bimetallic catalysts loaded on CeO2, which is used in experiments on low-temperature plasma-catalyzed CO2 methanation. This preparation method has the characteristics of easy preparation, large-scale production, solvent-free (dry milling) and environmentally friendly. The low-loaded Ni-Co alloy catalyst prepared by dry ball milling achieves high catalytic activity with the assistance of low-temperature plasma, which has not been reported in low-loaded alloy catalysts in low-temperature plasma-catalyzed CO2 methanation reactions. Summary of the invention

[0006] The present invention provides a method for preparing a nickel-based bimetallic catalyst based on a ball milling method. The preparation method of the present invention is simple, the plasma reaction experiment is easy to operate, the catalyst loading is low, the CO2 methanation reaction yield is high, and the catalytic activity effect is good. Different nickel-based alloy catalysts under low-temperature plasma conditions, and nickel-based alloy catalysts obtained by adding metal precursors in different sequences for ball milling have different CO2 conversion rates and methane selectivities. Among them, the catalyst of Ni-Co alloy loaded on CeO2 obtained by adding acetylacetonate nickel and acetylacetonate cobalt precursors simultaneously by ball milling has the best effect. The technical solution of the present invention is as follows: Preparation of Ni single metal catalyst: With CeO2 as the carrier, Ni as the active metal, and acetylacetonate as the metal precursor, nickel acetylacetonate and carrier CeO2 are added into a ball mill together and milled with grinding beads for 10 hours to obtain a catalyst which is recorded as Ni / CeO2.

[0007] Preparation of alloy catalyst: CeO2 is used as a carrier, the active metals are Ni, Co, Fe, and Mo, and the metal precursor is acetylacetonate metal salt. Nickel acetylacetonate and other different metal precursors and the carrier CeO2 are added to a ball mill and milled for 10 hours with grinding beads to obtain catalysts denoted as NiCo / CeO2-I, NiFe / CeO2-I, and NiMo / CeO2-I. The present invention also compares the effect of different Co contents in the NiCo alloy on the catalyst activity. The catalyst obtained by adding Ni and metal precursors with different Co contents and CeO2 to a ball mill and milling for 10 hours is NiCo. x / CeO2-I, subscript x is the mass percentage of metal Co. Finally, the catalyst obtained by first adding nickel acetylacetonate and CeO2 for ball milling for 10 hours and then adding cobalt acetylacetonate for ball milling for 10 hours is NiCo / CeO2-II. The catalyst obtained by first adding cobalt acetylacetonate and CeO2 for ball milling for 10 hours and then adding nickel acetylacetonate for ball milling for 10 hours is NiCo / CeO2-III. In this experiment, the ball milling speed, the calcination temperature of the ball-milled catalyst, the sieving mesh size, and the reduction temperature are all the same. The loading amount of metal Ni, Co, Fe and Mo in the Ni / CeO2, NiCo / CeO2-I, NiFe / CeO2-I, NiMo / CeO2-I, NiCo / CeO2-II and NiCo / CeO2-III catalysts described in the present invention is 0~1wt%, and the preferred metal loading amount is 1wt%.

[0008] The NiCo x In the / CeO2-I alloy catalyst, x=0.5~4, subscript x is the mass percentage of metal Co, preferably the metal Co content is 1wt%, and the metal Ni content is always maintained at 1wt%.

[0009] The ball mill jar of the present invention is preferably an agate jar, and the volume of the ball mill jar is 50-5000 ml, preferably 100 ml.

[0010] The ball mill beads of the present invention are preferably agate beads, with a large bead diameter of 0.8-1.5 cm and a small bead diameter of 0.3-0.6 cm. Preferably, the large bead diameter is about 1 cm and the small bead diameter is about 0.6 cm.

[0011] The total mass of the large and small ball mill beads of the present invention is preferably 47.5 g, and the quantity ratio of the large and small beads is preferably about 20:50.

[0012] The operation modes of the ball mill described in the present invention are preferably forward rotation, reverse rotation and stop rotation.

[0013] The ball milling time of the present invention is preferably 45 minutes of forward rotation, 45 minutes of reverse rotation, and 10 minutes of stop, with a total of 6 cycles, and a total ball milling time of 10 hours.

[0014] The ball milling speed of the present invention is 0-580 rpm, preferably 550 rpm.

[0015] The added amount of the carrier CeO2 described in the present invention can be 1~10g, and the preferred carrier mass is 3g.

[0016] The catalyst calcination temperature of the present invention is 300-900°C, preferably 500°C.

[0017] The calcination time described in the present invention is preferably 2 hours.

[0018] The catalyst screening size of the present invention is 10-60 mesh, preferably 30-40 mesh.

[0019] The hydrogen reduction temperature of the present invention is preferably 500° C., and the reduction time is preferably 2 h.

[0020] The hydrogen plasma reduction voltage of the present invention is 8-11 kV, preferably 9 kV.

[0021] The hydrogen content in the hydrogen thermal reduction and plasma reduction described in the present invention is preferably 20%.

[0022] The carrier gas used for hydrogen reduction described in the present invention is at least one of argon, nitrogen and helium.

[0023] The total flow rate of the raw gas CO2, H2 and Ar described in the present invention is 50~150ml / min, preferably 50ml / min.

[0024] The plasma reaction voltage of the present invention is 8-11 kV, preferably 10 kV.

[0025] Compared with the prior art, the above technical solution is adopted, and the beneficial effects of the present invention are as follows: The present invention adopts a ball milling method to prepare a catalyst with a loading of 2wt% of nickel-based bimetallic on CeO2. Among the prepared low-loading catalysts, the NiCo1 / CeO2-I catalyst has the best effect on low-temperature plasma-catalyzed CO2 hydrogenation to methane. In the experiment, the NiCo1 / CeO2-I catalyst retains the oxygen vacancies and surface alkalinity on the surface of CeO2, and achieves a high CO2 conversion rate (~60%) and methane selectivity / yield (~80% / ~50%). During the synthesis process, the effects of different nickel-based bimetallics on CO2 methanation under plasma catalysis were explored, and the effect of changes in the Co loading in the Ni-Co alloy on the catalytic performance was studied. Finally, the catalytic performance of the obtained Ni-Co alloy catalyst was adjusted by adding Ni and Co metal precursors simultaneously and sequentially. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Elemental HAADF structure diagram of the prepared Ni / CeO2, NiCo1 / CeO2-I, NiCo1 / CeO2-II, and NiCo1 / CeO2-III catalysts.

[0027] Figure 2 This is the elemental transmission electron microscopy (TEM) structure diagram of the prepared NiCo1 / CeO2-I catalyst.

[0028] Figure 3 High-resolution transmission electron microscopy (HRTEM) structure of the prepared NiCo1 / CeO2-I catalyst.

[0029] Figure 4 Catalyst evaluation results.

[0030] Figure 1 The catalysts corresponding to a, b, c, and d are: a-Ni / CeO2, b- NiCo1 / CeO2-I, c- NiCo1 / CeO2-II, d-NiCo1 / CeO2-III. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with embodiments, but the present invention is not limited to the following embodiments. Example

[0032] Preparation of Ni / CeO2 catalyst of the present invention: First, select a 100ml agate ball mill, then add 20 large agate grinding beads (1cm in diameter) and 50 small agate grinding beads (0.6cm in diameter) into the ball mill, with a total mass of 47.5g of grinding balls. Finally, add 0.1336g of nickel acetylacetonate and 3g of nano-cerium oxide into the ball mill, then add the same mass of grinding balls and drugs into another ball mill, place the two identical ball mills diagonally in the planetary ball mill, fix them with a fastener, and cover the ball mill lid. Set the program: forward 45min, reverse 45min, stop 10min, 6 cycles in total, a total ball milling time of 10h, and a rotation speed of 550rpm.

[0033] After the ball mill stops running, the ground catalyst precursor powder is taken out and placed in a porcelain boat, and calcined in air at 500°C for 2 h with a heating rate of 2°C / min. The calcined catalyst is sieved into 30-40 mesh. The sieved catalyst is placed in a tubular furnace and introduced with 20% H2 / N2 (50 ml / min). The temperature is adjusted to 500°C and reduced at a heating rate of 5°C / min for 2 h to obtain a Ni / CeO2 catalyst. Example

[0034] Preparation of NiCo / CeO2-I, NiFe / CeO2-I, NiMo / CeO2-I catalysts of the present invention: First, four 100ml agate ball mills were selected and marked as jars 1, 2, 3, and 4. Then, 20 large agate grinding beads (1 cm in diameter) and 50 small agate grinding beads (0.6 cm in diameter) were added to the four ball mills, with a total mass of 47.5 g. Then, 0.13395 g of nickel acetylacetonate and 3 g of nano-cerium oxide were added to jars 1, 2, and 3, respectively. Then, 0.12382 g of cobalt acetylacetonate was added to jar 1, and 0.194 was added to jar 2. 0g of ferric acetylacetonate was added to jar No. 3, 0.1040g of molybdenum acetylacetonate was added to jar No. 3, and 2 large agate grinding beads and one small agate grinding bead were added to jar No. 4 for counterweight. Finally, jars No. 1 and 2 as well as 3 and 4 were placed diagonally in the planetary ball mill, fixed with fasteners, covered with the ball mill lid, and run the set program: forward rotation for 45min, reverse rotation for 45min, stop rotation for 10min, and a total of 6 cycles. The total ball milling time is 10h and the rotation speed is 550rpm.

[0035] After the ball mill stopped running, the three ground catalyst precursor powders were taken out and placed in porcelain boats respectively, marked as No. 1, 2, and 3 porcelain boats corresponding to the catalysts in No. 1, 2, and 3 ball mill jars. They were calcined in air at 500°C for 2 h, with a heating rate of 2°C / min. The three catalysts after calcination were sieved into 30-40 mesh. The three sieved catalysts were respectively placed in a tubular furnace and introduced with 20% H2 / N2 (50 ml / min). The temperature was adjusted to 500°C and reduced at a heating rate of 5°C / min for 2 h to obtain NiCo1 / CeO2-I, NiFe1 / CeO2-I, and NiMo1 / CeO2-I catalysts.

[0037] NiCo of the present invention x Preparation of CeO2-I catalyst: First, select four 100ml agate ball mill jars, marked as jars 1, 2, 3, and 4, and then add 20 large agate grinding beads (diameter 1cm) and 50 small agate grinding beads (diameter 0.6cm) into the four ball mill jars, with a total mass of 47.5g. Then, add 0.13395g of nickel acetylacetonate and 3g of nano cerium oxide into jars 1, 2, and 3, respectively. Then, add 0.0669g of cobalt acetylacetonate into jar 1; add 0.12382g of acetylacetone into jar 2. cobalt; add 0.2697g of cobalt acetylacetonate into jar No. 3; add 0.13823g of nickel acetylacetonate, 0.5512g of cobalt acetylacetonate and 3g of nano cerium oxide into jar No. 4, finally place jars No. 1 and 2 as well as 3 and 4 diagonally in the planetary ball mill, fix them with fasteners, cover the ball mill lid, and run the set program: forward rotation for 45min, reverse rotation for 45min, stop rotation for 10min, and cycle 6 times in total. The total ball milling time is 10h and the rotation speed is 550rpm.

[0038] After the ball mill stopped running, the four ground catalyst precursor powders were taken out and placed in porcelain boats, respectively, and the porcelain boats were marked as No. 1, 2, 3, and 4, corresponding to the catalysts in the ball mill jars No. 1, 2, 3, and 4. They were calcined in air at 500°C for 2 h, with a heating rate of 2°C / min. The four calcined catalysts were sieved into 30-40 mesh. The four sieved catalysts were placed in a tubular furnace, respectively, and 20% H2 / N2 (50 ml / min) was introduced. The temperature was adjusted to 500°C and reduced at a heating rate of 5°C / min for 2 h to obtain NiCo 0.5 / CeO2-I, NiCo1 / CeO2-I, NiCo2 / CeO2-I, NiCo4 / CeO2-I catalysts.

[0039] Preparation of NiCo / CeO2-II and NiCo / CeO2-III catalysts of the present invention: First, select two ball mills, marked as ball mill No. 1 and ball mill No. 2, then add 20 large agate grinding beads (diameter 1 cm) and 50 small agate grinding beads (diameter 0.6 cm) into the two ball mills, with a total mass of 47.5 g. Then, add 3 g of nano cerium oxide to ball mill No. 1 and No. 2, respectively, and then add 0.13395 g of nickel acetylacetonate to ball mill No. 1; add 0.12382 g of cobalt acetylacetonate to ball mill No. 2. Finally, place ball mill No. 1 and No. 2 in a diagonal manner in a planetary ball mill, fix them with a fastener, cover the ball mill lid, and run the set program: forward for 45 minutes, reverse for 45 minutes, stop for 10 minutes, and cycle 6 times in total. The total ball milling time is 10 hours and the rotation speed is 550 rpm.

[0040] After the ball mill stops running, take out ball mill jars No. 1 and No. 2, and then add 0.12382 g of cobalt acetylacetonate to ball mill jar No. 1; add 0.13395 g of nickel acetylacetonate to ball mill jar No. 2. Finally, place ball mill jars No. 1 and No. 2 in the planetary ball mill in a diagonal manner, fix them with fasteners, cover the ball mill lid, and run the set program: forward rotation for 45 minutes, reverse rotation for 45 minutes, stop rotation for 10 minutes, and cycle 6 times in total. The total ball milling time is 10 hours and the rotation speed is 550 rpm.

[0041] After the ball mill stops running, the two ground precursor catalyst powders are taken out and placed in porcelain boats respectively, marked as No. 1, 2, and the porcelain boats correspond to the catalysts in No. 1, 2, and ball mill jars. They are calcined in air at 500°C for 2h, with a heating rate of 2°C / min. The two catalysts after calcination are sieved into 30-40 mesh. The two sieved catalysts are placed in a tubular furnace respectively, and 20% H2 / N2 (50ml / min) is passed through. The temperature is adjusted to 500°C and reduced at a heating rate of 5°C / min for 2h to obtain NiCo1 / CeO2-II and NiCo1 / CeO2-III.

[0042] Application Examples The plasma catalytic performance of Example 1 and Example 2 and Comparative Example 1 and Comparative Example 2 were verified respectively: Experimental steps: 300 mg of the catalyst prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were weighed on a balance. The DBD plasma reactor was a quartz cylinder (8 mm OD × 6 mm ID). A stainless steel rod with a diameter of 3 mm was used as the high-voltage electrode, and a copper mesh with a width of 2 cm was used as the ground electrode. 300 mg of the catalyst was placed on the top of the quartz wool between the high-voltage electrode and the low-voltage electrode. The catalyst was plasma reduced for 30 minutes in a 20% H2 / Ar (50 ml / min) gas flow. The reduction voltage and discharge frequency of the plasma were 9 kV and 7.7 kHz. After plasma reduction, the raw gas CO2, H2 and Ar (the volume percentage of the raw gas CO2 / H2 / Ar was 15% / 60% / 25%) was introduced at a total flow rate of 50 ml / min. Finally, the voltage of the power supply was adjusted so that the discharge voltage and discharge frequency were 10 kV and 7.7 kHz. The catalyst catalyzed the CO2 hydrogenation reaction at this voltage and frequency. The catalyst evaluation results are shown in the figure. Figure 4 shown.

[0043] from Figure 4It can be seen that the present invention explores the catalytic effect of different nickel-based bimetallic loadings on CeO2 on the low-temperature plasma CO2 hydrogenation reaction, and concludes that the NiCo1 / CeO2-I catalyst synthesized by simultaneously adding Ni and Co metal precursors and by ball milling has the best catalytic performance, and can have a higher CO2 conversion rate, CH4 selectivity and yield at a low metal loading.

Claims

1. A method for preparing a nickel-based bimetallic catalyst based on ball milling, characterized in that: Preparation of catalyst: The catalyst was prepared by dry ball milling, firstly, ball milling beads were added into a ball milling jar, then acetylacetone metal salt and nano-cerium oxide were added, and ball milling was performed in a planetary ball mill with set rotation speed and ball milling time. After ball milling, the obtained precursor powder was calcined, sieved and reduced with hydrogen to obtain a nickel-based bimetallic catalyst supported on cerium oxide; The grinding time of the planetary ball mill is 10 hours, during which the ball mill stops for 10 minutes every 90 minutes; the ball milling mode is forward rotation, reverse rotation and stop rotation, preferably forward rotation for 45 minutes, reverse rotation for 45 minutes, stop rotation for 10 minutes, and a total of 6 cycles; the ball milling speed is 0-580rpm, preferably 550rpm.

2. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (1), characterized in that: After the catalyst is prepared, screened and reduced, the catalyst is loaded into a dielectric barrier discharge (DBD) plasma reactor, and a mixed gas of Ar and H2 is introduced for plasma reduction. Finally, a certain proportion of raw gas of CO2, H2 and Ar is introduced, and a low-temperature plasma-catalyzed CO2 hydrogenation reaction occurs on the catalyst to produce CH4 and CO.

3. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (1), characterized in that: The acetylacetonate metal salt is nickel acetylacetonate or cobalt acetylacetonate. The ball mill of the catalyst is a planetary ball mill of the QM series. The rated speed of the ball mill is 280-600 rpm. The preferred model is QM-3SP2 with a rated speed of 580 rpm.

4. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (1), characterized in that: The ball mill jar is preferably made of agate, and the volume of the ball mill jar is 50-5000 ml, preferably 100 ml.

5. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (1), characterized in that: The grinding time of the planetary ball mill is 10 hours, during which the ball mill stops for 10 minutes every 90 minutes; the ball milling mode is forward rotation, reverse rotation and stop rotation, preferably forward rotation for 45 minutes, reverse rotation for 45 minutes, stop rotation for 10 minutes, and a total of 6 cycles; the ball milling speed is 0-580rpm, preferably 550rpm.

6. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (1), characterized in that: The calcination temperature of the catalyst is 500°C, the calcination time is 2h, the sieved catalyst is 30-40 mesh, the reduction temperature is 500°C, and the reduction time is 2h.

7. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (2), characterized in that: The dielectric barrier discharge DBD reactor is characterized in that the reactor is a cylindrical quartz tube reactor, with a stainless steel rod as the discharge electrode on the cylindrical axis, and a copper mesh with a width of 2 cm fixed by copper wire on the outside of the quartz tube reactor as the grounding electrode. The catalyst is fixed in the quartz tube by quartz wool, and a low-temperature plasma catalytic reaction occurs in the discharge area of ​​the copper mesh and the stainless steel rod.

8. The method for preparing a nickel-based bimetallic catalyst based on ball milling according to claim (2), characterized in that: The reaction of CO2 hydrogenation to produce methane is carried out under low-temperature plasma. The discharge voltage of the experiment is 8~11kV, the power is 8~12W, the total flow rate of plasma reducing gas Ar and H2 is preferably 50ml / min, and the volume percentage of reducing gas is Ar / H2=80% / 20%. The gases contained in the raw gas are CO2, H2 and Ar. The total flow rate of the raw gas is preferably 50ml / min, and the volume percentage of the raw gas is CO2 / H2 / Ar=15% / 60% / 25%.

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