CN111229235A - NiO/MgAl2O4Catalyst, preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a method for preparing MgAl by a ball milling method₂O₄The spinel supported NiO or Ni catalyst takes magnesium aluminate spinel as a carrier and NiO or Ni as an active component, wherein the mass of the active component accounts for NiO/MgAl₂O₄5-25% of the total mass of the catalyst. The active component of the catalyst obtained by roasting after ball milling is NiO, and the catalyst can be used for catalytic combustion reaction of low-concentration methane or volatile organic gas. And reducing NiO to obtain the supported Ni metal catalyst which can be used for hydrogenation of organic unsaturated bonds or steam or water phase reforming reaction of the organic matter. The catalyst of the invention can be used for catalytic combustion of low-concentration methane or volatile organic gasBurning, organic matter hydrogenation or reforming hydrogen production. Compared with the prior art, the catalyst has the advantages of high activity, low cost, good thermal stability, simple preparation method, environmental protection, reduction of wastewater discharge and easy industrialization.

Description

NiO/MgAl2O4 catalyst and its preparation method and application

technical field

The invention belongs to the technical field of catalyst preparation, in particular to a NiO/MgAl ₂ O ₄ catalyst and a preparation method and application thereof.

Background technique

Nickel catalysts are not only good catalysts for oxidative dehydrogenation, dehalogenation, desulfurization and other transformation processes, but also widely used in various unsaturated hydrocarbons due to their good catalytic activity, high mechanical strength, insensitivity to poisons, and good thermal conductivity. Hydrogenation and reforming of organics to produce hydrogen. Nickel catalysts are inexpensive and readily available, and have great potential for industrial application.

When the nickel catalyst is supported on a suitable carrier, the nickel active species will form an ordered whole with the support, thereby effectively improving the activity and stability of the catalyst. This whole is called a supported nickel catalyst. The carrier increases the active surface of the catalyst, provides a suitable pore structure for the active component, and makes it have a good dispersion state so as to reduce the amount of the active component. At the same time, the carrier can improve the mechanical strength, thermal conductivity and thermal stability of the catalyst, and prolong the service life of the catalyst. In addition to providing the active center itself, the carrier can also improve the catalyst performance by interacting with the active components. The most commonly used support for supported nickel catalysts is γ-Al ₂ O ₃ . γ-Al ₂ O ₃ has good mechanical properties and regeneration performance, and is inexpensive, but the strong interaction between it and transition metal oxides limits the further improvement of the catalytic activity of active components. Adding other oxides to γ-Al ₂ O ₃ for modulation can reduce the strength of the interaction with the active components, reduce the formation of the difficult-to-reduce NiAl ₂ O ₄ nickel-aluminum spinel structure, and improve the catalyst performance. If MgO is added to γ-Al ₂ O ₃ to form a stable MgAl ₂ O ₄ magnesia-aluminum spinel structure, the interaction strength between the active component nickel and the carrier will be reduced. In addition, magnesia-alumina spinel not only combines the advantages of both γ-Al ₂ O ₃ and MgO oxides, but also possesses new advantages, such as better thermal stability, mechanical strength, and hydration resistance. However, magnesium-aluminum spinel requires a high roasting temperature, and the surface of the catalyst magnesium-aluminum spinel prepared by common methods will still form a nickel-aluminum spinel structure, and the utilization efficiency of nickel is not high. Therefore, the current magnesium-aluminum spinel Stones are not widely used in supported nickel catalysts.

The preparation method of the catalyst will have a great influence on its activity and stability. Even if the active components and loading of the catalyst are exactly the same, the catalytic performance will be different due to different preparation methods and conditions. At present, the most common preparation methods of supported nickel catalysts are co-precipitation method, impregnation method, sol-gel method and solution combustion method. The active components of the catalyst prepared by the co-precipitation method and the impregnation method are unevenly distributed; the sol-gel method has a long preparation period and is prone to pollution; the solution combustion method has poor controllability. These common methods all produce waste water or waste gas pollution, which has an impact on the environment.

Supported nickel catalysts are widely used in various reaction processes: ① Hydrogenation of organic matter. Nickel catalyst has high activity and good CH ₄ selectivity in CO _x hydromethanation reaction, and is currently the most popular methanation catalyst; aniline tar hydrocracking reaction can reach 100% aniline tar cracking rate under the catalysis of nickel catalyst; Pyrolysis gasoline needs to undergo two-stage hydrogenation before it can be used as the raw material for aromatics extraction. Nickel catalyst has become the main one-stage hydrogenation catalyst due to its excellent resistance to arsenic and gum. ②Organic catalytic reforming. The nickel catalyst shows good activity and selectivity in the CH ₄ -CO ₂ reforming reaction; the nickel catalyst has a low activity temperature in the steam reforming of methane, n-butane and other organic compounds, which can reduce the content of methane and CO in the product. ③ catalytic oxidation of organic matter. Nickel catalysts can significantly improve the ethylene yield in the oxidative dehydrogenation of ethane. The yield of isobutene in the isobutane dehydrogenation reaction was significantly improved over nickel catalysts.

Volatile organic compounds (VOCs) and low-concentration methane are air pollutants that exist widely in factories or coal mines, and have environmental protection requirements for purification treatment. Among them, the molecular structure of methane is stable, the oxidation difficulty is the greatest among organic gases, and the reaction temperature is the highest, which requires higher activity and stability of the catalyst. Catalytic combustion can achieve high-efficiency conversion of organic matter into _CO2 and water at lower temperature and obtain its energy without secondary pollution. At the same time, the catalytic combustion is sufficient, the space velocity is high, and there is no concentration limit. Therefore, the catalyst developed based on the catalytic combustion of low-concentration methane can also be applied to the occasions of general hydrocarbon organic gases that do not contain heteroatoms such as S, Cl and N. Supported nickel catalysts are widely used in the catalytic oxidation of organic compounds, and also have catalytic activity for the catalytic combustion of low-concentration methane, and the nickel sources are widely available and inexpensive, and have application potential. However, the activity of nickel catalyst for catalytic oxidation of low-concentration methane is not outstanding, the thermal stability is insufficient, and the common preparation methods will produce waste water, so the economy needs to be improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a NiO/MgAl ₂ O ₄ catalyst with excellent catalytic activity and thermal stability, and a preparation method and application thereof, which do not produce waste water, in order to overcome the above-mentioned defects of the prior art.

The object of the present invention can be achieved through the following technical solutions: a NiO/MgAl ₂ O ₄ catalyst, characterized in that, a magnesium aluminum spinel is used as a carrier, and NiO or Ni is used as an active component, wherein the active component The mass of NiO/MgAl 2 O 4 accounts for 5-25% of the total mass of the NiO/MgAl ₂ O ₄ catalyst.

Further, the magnesium-aluminum spinel is a commercially available product.

Further, described magnesium aluminum spinel is made by the following method:

Step 1: Weigh Mg(NO ₃ ) ₂ .6H ₂ O and Al(NO ₃ ) ₃ .9H ₂ O according to n(Mg):n(Al)=1:2, and dissolve them in aqueous ethanol to prepare a total of A solution with a concentration of 0.1 to 1 mol·L ^-1 ;

Step 2: Weigh the precipitant whose mole number is (1～1.3)∑niXi, wherein ni is the mole number of metal ions, Xi is the valence of metal ions, dissolve in ethanol aqueous solution, and configure into a solution with the same volume as the solution in step 1;

Step 3: At the same time, the solution obtained in steps 1 and 2 is fed into the reactor at a constant speed with a sampling pump, stirred vigorously, aged at a constant temperature of 50-70 °C for 2-4 hours, filtered, dried at 100-120 °C, and ground for 80-100 Mesh sieve, the sieved powder is placed in a muffle furnace for calcination at 800-1000 DEG C for 3-6 hours to obtain a magnesia-aluminum spinel carrier.

The above-mentioned co-precipitation synthesis method of MgAl ₂ O ₄ magnesia-aluminum spinel carrier can also be replaced by other synthesis methods. Said other synthesis method is selected from urea method, hydrothermal synthesis method and solution combustion synthesis method.

Further, the ethanol mass fraction of the ethanol aqueous solution is 0-50%

Further, in step 2, the precipitating agent is selected from one or a mixture of Na ₂ CO ₃ , (NH ₄ ) ₂ CO ₃ , NaOH, and KOH.

A preparation method of NiO/MgAl ₂ O ₄ catalyst for catalytic combustion of organic matter, the carrier powder and nickel salt powder are mixed, placed in a ball mill tank, and grinding beads are added, and the ball-to-material ratio is the ratio of the mass of the grinding beads to the material. It is 1:1～6:1; the ball mill tank is sealed and fixed on the turntable of the planetary ball mill. After passing through a sieve of 80-100 meshes, the sieved powder is placed in a tube furnace for calcination at 600-800 DEG C for 3-6 hours to obtain a NiO/MgAl ₂ O ₄ catalyst.

On the basis of the main catalyst Ni, other components, such as Fe, Mn, Ce, La, Zr, Cu and other metal precursors can also be added as co-catalysts during ball milling. The addition of metal additives can not only improve the dispersion of Ni, disperse the electron distribution of Ni atoms, effectively protect and stabilize Ni nanoparticles, but also synergize with Ni to improve the catalyst activity. After Fe is added, it forms a stable Fe-Ni alloy with Ni, which is beneficial to the dispersion of Ni on the surface of the carrier. The more active Fe protects Ni from being corroded by acid, which improves the activity of the catalyst and the stability against acid; the addition of Mn reduces the activity. The force between the components and the carrier increases the number of medium-strength active centers and improves the activity and stability of the catalyst; when Ce is added in the form of CeO ₂ , part of Ce ⁴⁺ is reduced to Ce ³⁺ at high temperature. Electron-rich oxygen vacancies, the free electrons released are transferred to the ^Ni active site to increase the electron density around it and promote the reduction of Ni species, while the redox properties of CeO accelerate the transfer of surface _- adsorbed carbon-containing species and improve catalyst anti-accumulation Carbon properties; La promotes the dispersion of NiO on the surface of the carrier, weakens the interaction between the active component and the carrier, and inhibits the formation of nickel-aluminum spinel; the addition of Zr-containing additives significantly improves the adsorption capacity of the catalyst for specific reactants, thereby improving the Catalyst activity and selectivity; Cu can be reduced to copper nuclei at a lower temperature, and then acts as the nucleation of adjacent NiO to increase the nucleation rate of NiO and promote the reduction of NiO, and Cu can also promote the formation of nickel species in the support. The dispersion on the catalyst improves the stability of the catalyst.

The grinding beads are 95 zirconium beads with a diameter of 2-10 mm.

The nickel salt is one or a mixture of nickel nitrate hexahydrate, nickel acetate tetrahydrate, nickel formate dihydrate, nickel oxalate dihydrate, and nickel citrate hydrate. Inorganic nickel salts such as nickel nitrate hexahydrate have high hardness, and the color of the catalyst prepared by ball milling is uneven, which is not conducive to industrial application, while organic nickel salts are soft and suitable for catalyst preparation by ball milling, so organic nickel salts are preferred as the nickel source. Among them, the dispersion degree of Ni element in the nickel acetate tetrahydrate crystal is relatively high, the NiO crystal grains formed on the catalyst surface are smaller, and the obtained catalyst activity is relatively prominent. Therefore, nickel acetate tetrahydrate is further preferred as a suitable nickel source.

The present invention also provides an application of the above-mentioned NiO/MgAl ₂ O ₄ catalyst in the catalytic combustion of low-concentration methane or volatile organic gas, comprising the following steps: in a fixed-bed reactor, using low-concentration methane or volatile organic gas It is a reaction gas, and the catalytic combustion reaction is carried out under the action of NiO/MgAl ₂ O ₄ catalyst; the flow rate of the reaction gas is 10～100Nml·min ^-1 , the content of methane or volatile organic compounds is 1～20vol%, and the temperature is 1～2℃·min ^-1 The temperature is raised to a reaction temperature of 550 to 750° C., and the pressure of the reaction system is 1 to 2 MPa.

Further, the NiO/MgAl ₂ O ₄ catalyst prepared by the ball milling method is reduced to obtain a supported Ni metal catalyst, that is, the Ni/MgAl ₂ O ₄ catalyst can be used for the hydrogenation of organic unsaturated bonds or organic matter steam or water-phase reforming reaction. , including the following steps: put the NiO/MgAl ₂ O ₄ catalyst obtained by ball milling into a fixed-bed reactor, and under the nitrogen purge with a flow rate of 30-100 Nml·min ^-1 , the temperature is increased at 1~10°C·min ^-1 to 200～300℃, then switch to reducing gas with a flow rate of 30～100Nml·min ^-1 , reducing gas at 10～100vol.% H ₂ /N ₂ , and heat up to 450～700 at 1～10℃·min ^-1 The reduction of the catalyst is carried out at ℃; the reduction time is 2-4 h, and the reduction pressure is 1-2 MPa to obtain a Ni/MgAl ₂ O ₄ catalyst.

Further, using the Ni/MgAl ₂ O ₄ catalyst for the hydrogenation reaction of organic unsaturated bonds includes the following steps: when the reduction of the Ni/MgAl ₂ O ₄ catalyst in the fixed bed reactor is completed and the temperature has not been lowered, switch to a flow rate of 30-100 Nml Nitrogen purge for min ^-1 , adjust the temperature to 300-550°C, switch to a reaction gas with a flow rate of 50-200 Nml min ^-1 , the reaction gas is a mixture of preheated unsaturated organic matter and _H2 , The hydrogenation reaction is carried out under the action of Ni/MgAl ₂ O ₄ catalyst; the pressure of the reaction system is 1-2MPa.

Further, using the Ni/MgAl ₂ O ₄ catalyst for the organic steam or water-phase reforming reaction includes the following steps: when the reduction of the Ni/MgAl ₂ O ₄ catalyst in the fixed bed reactor is completed and the temperature has not been lowered, switch to a flow rate of 30 Purge with ～100Nml·min ^-1 of nitrogen, adjust the temperature to 550～650℃, switch to the reaction gas with a flow rate of 10～100Nml·min ^-1 , the reaction gas is the gas preheated from the organic matter aqueous solution or the preheated organic matter The mixed gas of gas and water vapor is reformed under the action of Ni/MgAl ₂ O ₄ catalyst; the pressure of the reaction system is 1MPa.

Compared with the prior art, the advantages of the present invention are:

(1) The present invention selects magnesia-aluminum spinel as the carrier, and prepares the catalyst with the required activity and thermal stability by ball milling. By selecting suitable precursors and preparation conditions, a suitable force can be generated between the carrier and the active ingredients, and the catalysts with activity and stability are far higher than those prepared by traditional methods such as precipitation or impregnation. At the same time, considering that the ball milling method does not require a solution environment, insoluble precursors can be used, and no waste water is generated, which has advantages in the preparation of the catalyst.

(2) The MgAl ₂ O ₄ magnesia-aluminum spinel carrier of the catalyst of the present invention has large specific surface area and pore volume, and strong heat resistance, so that the catalytic activity and thermal stability of the catalyst are significantly improved. When the catalyst of the invention is used for the catalytic combustion reaction of low concentration methane, the pseudo-first-order reaction rate constant measured at 600° C. is 0.2-0.5 L·g-Ni ^-1 ·s ^-1 , and the reaction temperature when the conversion rate is 50% is 540～570℃.

(3) The present invention adopts the ball milling method to prepare, does not need a solution environment, can use insoluble precursors, and does not generate waste water; the prepared powder has a small particle size and a large specific surface area. The preparation method is simple, easy to be industrialized, does not generate waste water, has little pollution, and is favorable for large-scale industrial production.

(4) The cost is greatly reduced, and the raw material is the cheap nickel element.

Description of drawings

FIG. 1 is the XRD pattern of the MgAl ₂ O ₄ magnesium aluminum spinel carrier and the NiO/MgAl ₂ O ₄ catalyst in Example 2 of the present invention.

2 is the H ₂ -TPR spectrum of the MgAl ₂ O ₄ magnesia-aluminum spinel carrier and the NiO/MgAl ₂ O ₄ catalyst in Example 2 of the present invention.

Figure 3 is the methane conversion curve of the NiO/MgAl ₂ O ₄ catalyst cycled three times (R1, R2, R3) in Example 2 of the present invention.

Detailed ways

The following examples are used to illustrate the present invention, but are not intended to limit the protection scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples are conventional methods unless otherwise specified.

The phase structure of the samples was analyzed using a D/max-2200/PC X-ray diffractometer from Rigaku Corporation. The test conditions are: Cu target (λ=0.154056nm), scanning range 10o-90o, scanning step 0.005o, scanning speed 5o·min ^-1 , tube voltage 40kV, tube current 40mA.

The samples were tested for H ₂ -TPR using PCA-1200 chemisorption analyzer from Beijing Biode Electronics Co., Ltd.

Common indicators to measure catalyst performance include T ₅₀ , k ₆₀₀ , and Ea. T ₅₀ is the reaction temperature at which the methane conversion is 50%. At low concentrations, the reaction rate is first-order with the methane concentration. From the corresponding methane conversion rates (x,-) at different reaction temperatures (T, °C), the pseudo-first-order reaction rate constant k, L·g ^-1 ·s ^-1 can be calculated at this temperature:

In the formula: L is the reaction gas flow rate under standard conditions, L·s ^-1 ; w is the mass of the catalyst active component (NiO), g; R is the molar gas constant, 8.314J·(mol·K) ^-1 ; A is the pre-exponential factor, L·g ^-1 ·s ^-1 ; Ea is the activation energy of the reaction, kJ·mol ^-1 . k ₆₀₀ is the k value at T=600°C, and the higher k ₆₀₀ is, the higher the specific activity of the catalyst. Ea can be calculated by correlating the k values at different temperatures using the least squares method.

Example 1

A NiO/MgAl 2 O 4 catalyst for low-concentration methane catalytic combustion, the NiO/MgAl ₂ O ₄ catalyst uses MgAl ₂ O ₄ magnesium aluminum spinel as a carrier and NiO as an active component, wherein the NiO/MgAl ₂ O ₄ catalyst is The mass of active components accounts for 5% of the total mass of the NiO/MgAl ₂ O ₄ catalyst.

The preparation method of the above-mentioned NiO/MgAl ₂ O ₄ catalyst comprises the following steps:

Step 1: Weigh 7.0 g of Mg(NO ₃ ) ₂ ·6H ₂ O and 20.3 g of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve them in 200 g of deionized water, and prepare a total concentration of 0.4 mol · L ^-1 solution.

Step 2: Weigh 12.6 g of sodium carbonate, dissolve it in 200 mL of deionized water, and prepare a solution with the same volume as the solution in step 1.

Step 3: At the same time, the solution obtained in steps 1 and 2 was fed into the reactor at a constant speed with a sample pump, stirred vigorously, aged at 70 °C for 3 hours, filtered, dried at 100 °C, ground through an 80-mesh sieve, and the sieved powder was placed in the reactor. The MgAl ₂ O ₄ magnesia-aluminum spinel carrier is obtained by calcining at 1000℃ for 6h in a muffle furnace.

Step 4: Mix 5g of the carrier powder in step 3 with 1.0g of nickel nitrate hexahydrate solid, place it in a ball mill, add grinding beads (95 zirconium beads, diameter 4mm), ball-to-material ratio (the ratio of the mass of the grinding beads to the material) ) is 4:1. The ball mill jar is sealed and fixed on the turntable of the planetary ball mill. The rotation speed (800rpm) and the rotation mode (alternating direction every 30min) are set. After ball milling for 8 hours, the powder in the jar is ground and passed through an 80-mesh sieve. The sieved powder was calcined at 650°C for 6h in a tube furnace to obtain a NiO/MgAl ₂ O ₄ catalyst, which was called Cat.1.

The XRD patterns of MgAl ₂ O ₄ magnesium aluminum spinel support and NiO/MgAl ₂ O ₄ catalyst are shown in Fig. 1 . Figure 2 shows the H ₂ -TPR spectra of MgAl ₂ O ₄ magnesium aluminum spinel support and NiO/MgAl ₂ O ₄ catalyst.

Example 2

A NiO/MgAl 2 O 4 catalyst for low-concentration methane catalytic combustion, the NiO/MgAl ₂ O ₄ catalyst uses MgAl ₂ O ₄ magnesium aluminum spinel as a carrier and NiO as an active component, wherein the NiO/MgAl ₂ O ₄ catalyst is The mass of the active components accounted for 10% of the total mass of the NiO/MgAl ₂ O ₄ catalyst.

The preparation method of the above-mentioned NiO/MgAl ₂ O ₄ catalyst comprises the following steps:

Step 1: Weigh 16.5 g of Mg(NO ₃ ) ₂ ·6H ₂ O and 48.3 g of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve them in 200 g of ethanol aqueous solution (25% ethanol mass fraction), and prepare a total of A solution with a concentration of 0.8 mol·L ^-1 .

Step 2: Weigh 32.2 g of ammonium carbonate, dissolve it in 240 mL of ethanol aqueous solution (25% ethanol mass fraction), and prepare a solution with the same volume as the solution in step 1.

Step 3: At the same time, the solution obtained in steps 1 and 2 is fed into the reactor at a constant speed with a sampling pump, stirred vigorously, aged at 65°C for 4 hours, filtered, dried at 110°C, ground and passed through a 100-mesh sieve, and the sieved powder was placed in the reactor. The MgAl ₂ O ₄ magnesia-aluminum spinel carrier was obtained by calcining at 900° C. for 4 hours in a muffle furnace.

Step 4: Mix 5g of the carrier powder with 1.9g of solid nickel acetate tetrahydrate in step 3, place it in a ball mill, add grinding beads (95 zirconium beads, 6 mm in diameter), and the ratio of the ball to the material (the mass ratio of the grinding beads to the material) ) is 2:1. The ball mill jar is sealed and fixed on the turntable of the planetary ball mill. The rotation speed (400rpm) and the rotation mode (alternating direction every 15min) are set. After ball milling for 4 hours, the powder in the jar is ground and passed through a 100-mesh sieve. The sieved powder was calcined at 700°C for 4h in a tube furnace to obtain a NiO/MgAl ₂ O ₄ catalyst, which was called Cat.2.

Example 3

A NiO/MgAl 2 O 4 catalyst for low-concentration methane catalytic combustion, the NiO/MgAl ₂ O ₄ catalyst uses MgAl ₂ O ₄ magnesium aluminum spinel as a carrier and NiO as an active component, wherein the NiO/MgAl ₂ O ₄ catalyst is The mass of active components accounted for ₁₅ % of the total mass of the NiO/ _MgAl2O4 catalyst.

The preparation method of the above-mentioned NiO/MgAl ₂ O ₄ catalyst comprises the following steps:

Step 1: Weigh 12.1 g of Mg(NO ₃ ) ₂ ·6H ₂ O and 35.3 g of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve them in 200 g of ethanol aqueous solution (50% ethanol mass fraction), and prepare a total of A solution with a concentration of 0.6 mol·L ^-1 .

Step 2: Weigh 15.1 g of sodium hydroxide, dissolve it in 240 mL of ethanol aqueous solution (50% ethanol mass fraction), and prepare a solution with the same volume as the solution in step 1.

Step 3: At the same time, the solution obtained in steps 1 and 2 was fed into the reactor at a constant speed with a sample pump, stirred vigorously, aged at a constant temperature of 55 °C for 2 hours, filtered, dried at 100 °C, ground and passed through a 90-mesh sieve, and the sieved powder was placed in the reactor. The MgAl ₂ O ₄ magnesia-aluminum spinel carrier was obtained by calcining at 800°C for 3 hours in a muffle furnace.

Step 4: Mix 5g of the carrier powder in step 3 with 2.2g of nickel formate dihydrate solid, place it in a ball mill jar, add grinding beads (95 zirconium beads, diameter 10mm), ball-to-material ratio (the ratio of the mass of the grinding beads to the material) ) is 6:1. The ball mill jar is sealed and fixed on the turntable of the planetary ball mill. The rotation speed (700rpm) and the rotation mode (alternating direction every 30min) are set. After ball milling for 7 hours, the powder in the jar is ground and passed through a 90-mesh sieve. The sieved powder was calcined at 800°C for 5h in a tube furnace to obtain a NiO/MgAl ₂ O ₄ catalyst, which was called Cat.3.

Example 4

A NiO/MgAl 2 O 4 catalyst for low-concentration methane catalytic combustion, the NiO/MgAl ₂ O ₄ catalyst uses MgAl ₂ O ₄ magnesium aluminum spinel as a carrier and NiO as an active component, wherein the NiO/MgAl ₂ O ₄ catalyst is The mass of active components accounts for 20% of the total mass of the NiO/MgAl ₂ O ₄ catalyst.

The preparation method of the above-mentioned NiO/MgAl ₂ O ₄ catalyst comprises the following steps:

Step 1: Weigh 22.5 g of Mg(NO ₃ ) ₂ ·6H ₂ O and 66.0 g of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve them in 200 g of ethanol aqueous solution (25% ethanol mass fraction), and prepare the total A solution with a concentration of 1.0 mol·L ^-1 .

Step 2: Weigh 39.5 g of potassium hydroxide, dissolve it in 260 mL of ethanol aqueous solution (25% ethanol mass fraction), and prepare a solution with the same volume as the solution in step 1.

Step 3: At the same time, the solution obtained in steps 1 and 2 was fed into the reactor at a constant speed with a sample pump, stirred vigorously, aged at 60°C for 4 hours, filtered, dried at 120°C, ground and passed through a 100-mesh sieve, and the sieved powder was placed in the reactor. The MgAl ₂ O ₄ magnesia-aluminum spinel carrier was obtained by calcining at 900° C. for 4 hours in a muffle furnace.

Step 4: Mix 5g of the carrier powder in step 3 with 2.5g of nickel oxalate dihydrate solid, place it in a ball mill, add grinding beads (95 zirconium beads, 2 mm in diameter), and the ratio of the ball to the material (the mass ratio of the grinding beads to the material) ) is 3:1. The ball mill jar is sealed and fixed on the turntable of the planetary ball mill. The rotation speed (500rpm) and the rotation mode (alternating direction every 15min) are set. After ball milling for 6 hours, the powder in the jar is ground and passed through a 100 mesh sieve. The sieved powder was calcined at 750°C for 3h in a tube furnace to obtain a NiO/MgAl ₂ O ₄ catalyst, which was called Cat.4.

Example 5

A NiO/MgAl 2 O 4 catalyst for low-concentration methane catalytic combustion, the NiO/MgAl ₂ O ₄ catalyst uses MgAl ₂ O ₄ magnesium aluminum spinel as a carrier and NiO as an active component, wherein the NiO/MgAl ₂ O ₄ catalyst is The mass of active components accounts for ₂₅ % of the total mass of the NiO/ _MgAl2O4 catalyst.

The preparation method of the above-mentioned NiO/MgAl ₂ O ₄ catalyst comprises the following steps:

Step 1: Weigh 3.5g of Mg(NO ₃ ) ₂ ·6H ₂ O and 10.2g of Al(NO ₃ ) ₃ ·9H ₂ O, dissolve them in 200g of ethanol aqueous solution (50% ethanol mass fraction), and prepare the total A solution with a concentration of 0.2 mol·L ^-1 .

Step 2: Weigh 7.0 g of sodium carbonate, dissolve it in 200 mL of ethanol aqueous solution (50% ethanol mass fraction), and prepare a solution with the same volume as the solution in step 1.

Step 3: At the same time, the solution obtained in steps 1 and 2 was fed into the reactor at a constant speed with a sampling pump, stirred vigorously, aged at a constant temperature of 50 °C for 2 hours, filtered, dried at 120 °C, ground through an 80-mesh sieve, and the sieved powder was placed in the reactor. The MgAl ₂ O ₄ magnesia-aluminum spinel carrier is obtained by calcining at 1000℃ for 6h in a muffle furnace.

Step 4: Mix 5 g of the carrier powder in step 3 with 4.1 g of nickel citrate hydrate solid, place it in a ball mill, add grinding beads (95 zirconium beads, 8 mm in diameter), and the ratio of ball to material (the mass of the grinding beads and the material) ratio) is 5:1. The ball mill jar is sealed and fixed on the turntable of the planetary ball mill, and the rotation speed (300rpm) and the rotation mode (fixed rotation direction) are set. The sieved powder was calcined at 600°C for 6h in a tube furnace to obtain a NiO/MgAl ₂ O ₄ catalyst, which was called Cat.5.

Table 1 shows the activity data of Cat. 1-5 catalysts. It can be seen that for low-concentration methane catalytic combustion reaction, the k ₆₀₀ of the catalyst prepared from the organic nickel source is 0.2-0.5 L·g-Ni ^-1 ·s ^-1 , the T ₅₀ is 540-570 ℃, and the Ea is 130-170 kJ ·mol ^-1 , especially the catalyst Cat.2 prepared with nickel acetate tetrahydrate as the nickel source has a k ₆₀₀ as high as 0.489L·g-Ni ^-1 ·s ^-1 , and a T ₅₀ as low as 543.5℃. It can be seen that the NiO/MgAl ₂ O ₄ catalyst prepared by the present invention has good catalytic activity.

Table 1 Activity data of catalysts with different numbers

FIG. 3 is the methane conversion curve of the catalyst obtained in Example 2 with three cycles (R1, R2, R3). It can be seen that the activity of the catalyst is slightly improved each time it is used for three cycles, its k ₆₀₀ remains above 0.4L·g-Ni ^-1 ·s ^-1 , and its T ₅₀ is between 540 and 560°C. It can be seen that the NiO/MgAl ₂ O ₄ catalyst prepared by the present invention has good thermal stability.

Example 6

The 0.15g NiO/MgAl ₂ O ₄ catalyst prepared in Example 2 was placed in the constant temperature zone of the fixed bed reactor, with low concentration methane as the reaction gas, the flow rate of the reaction gas was 50 Nml·min ^-1 , and the methane content was 1 vol%. The fixed-bed reactor was heated by programmed heating, heated to 300°C at a rate of 2°C·min ^-1 , heated to 600°C at a rate of 1°C·min ^-1 after constant temperature for 40 minutes, and stopped heating after constant temperature for 1 minute. The second and third activity tests were followed by cooling to room temperature in the reaction gas stream.

FIG. 3 is the methane conversion curve of the catalyst obtained in Example 2 with three cycles (R1, R2, R3). It can be seen that the activity of the catalyst is slightly improved each time it is used for three cycles, its k ₆₀₀ remains above 0.4L·g-Ni ^-1 ·s ^-1 , and its T ₅₀ is between 540 and 560°C. It can be seen that the NiO/MgAl ₂ O ₄ catalyst prepared by the present invention has good thermal stability.

Example 7

The 0.5g NiO/MgAl ₂ O ₄ catalyst prepared in Example 2 was placed in the constant temperature zone of the fixed-bed reactor, and the flow rate was 50 Nml·min ⁻¹ of nitrogen purging, and the temperature was raised to 200° C. at 2° C.·min ⁻¹ . Then switch to the reducing gas with a flow rate of 50Nml·min ^-1 , the reducing gas is 50vol.% H ₂ /N ₂ , and the temperature is raised to 550°C at 1°C·min ^-1 to reduce the catalyst; the reduction time is 4h, and the reduction pressure is 2MPa. When the reduction of the Ni/MgAl ₂ O ₄ catalyst is completed and the temperature is not lowered, switch to nitrogen purging with a flow rate of 50 Nml·min ^-1 , and when the temperature drops to 400 °C, switch to a reaction gas with a flow rate of 100 Nml·min ^-1 , the reaction gas is A mixture of CO and H ₂ volume ratio of 1:3 has been preheated to 200 °C. The pressure of the reaction system was 2MPa. The hydrogenation reaction was carried out under the action of Ni/MgAl ₂ O ₄ catalyst. After cooling and drying, the product gas was analyzed by Zhejiang Fuli GC9070 gas chromatograph. The results show that the conversion of CO reaches 100%, and the selectivity of _CH4 in the product reaches 96%. After the reaction was carried out for 24 h, the CO conversion rate was 96%, and the CH ₄ selectivity was 94%; after the reaction was carried out for 100 h, the CO conversion rate was 90%, and the selectivity was 85%. It can be seen that the Ni/MgAl ₂ O ₄ catalyst prepared by the present invention has good activity and stability.

Example 8

The 1g NiO/MgAl ₂ O ₄ catalyst prepared in Example 2 was placed in the constant temperature zone of the fixed-bed reactor, and the flow rate was 30 Nml·min ⁻¹ under nitrogen purging, and the temperature was raised to 300° C. at 5° C.·min ⁻¹ , and then Switch to a reducing gas with a flow rate of 30Nml·min ^-1 , pure H ₂ , and the catalyst is reduced at a temperature of 2℃·min ^-1 to 650℃; the reduction time is 2h, and the reduction pressure is 1MPa. When the reduction of the Ni/MgAl ₂ O ₄ catalyst is completed and the temperature is not lowered, switch to nitrogen purging with a flow rate of 30 Nml·min ^-1 , and when the temperature drops to 600 °C, switch to a reaction gas with a flow rate of 20 Nml·min ^-1 , the reaction gas is A 50% mass fraction of ethanol aqueous solution is preheated to a gas at 200°C. The pressure of the reaction system was 1 MPa. The reforming reaction was carried out under the action of Ni/MgAl ₂ O ₄ catalyst. After cooling and drying, the product gas was analyzed by Zhejiang Fuli GC9070 gas chromatograph. The results showed that the conversion of ethanol reached 100% at 500°C, and the selectivity of _H2 in the product was 50% at 500°C and 72% at 600°C. It can be seen that the Ni/MgAl ₂ O ₄ catalyst prepared by the present invention has good catalytic activity.

The above-mentioned embodiments are only preferred embodiments of the present invention, and are only used to explain the present invention, but not to limit the scope of implementation of the present invention. It is easy to make other embodiments by replacing or changing the technical content, so all changes and improvements made in the principles and process conditions of the present invention should be included in the scope of the patent application of the present invention.

Claims (10)

1. a NiO/MgAl ₂ O ₄ catalyst, it is characterized in that, with magnesia-aluminum spinel as carrier, with NiO or Ni as active component, wherein the quality of said active component accounts for NiO/MgAl ₂ O ₄ catalyst 5 to 25% of the total mass. 2 . The NiO/MgAl ₂ O ₄ catalyst according to claim 1 , wherein the magnesium-aluminum spinel is a commercially available product. 3 . 3. a kind of NiO/MgAl ₂ O ₄ catalyst according to claim 1, is characterized in that, described magnesia-aluminum spinel is made by the following method: Step 1: Weigh Mg(NO ₃ ) ₂ .6H ₂ O and Al(NO ₃ ) ₃ .9H ₂ O according to n(Mg):n(Al)=1:2, and dissolve them in aqueous ethanol to prepare a total of A solution with a concentration of 0.1 to 1 mol·L ^-1 ; Step 2: Weigh the precipitant whose mole number is (1～1.3)∑niXi, wherein ni is the mole number of metal ions, Xi is the valence of metal ions, dissolve in ethanol aqueous solution, and configure into a solution with the same volume as the solution in step 1; Step 3: At the same time, the solution obtained in steps 1 and 2 is fed into the reactor at a constant speed with a sampling pump, stirred vigorously, aged at a constant temperature of 50-70 °C for 2-4 hours, filtered, dried at 100-120 °C, and ground for 80-100 Mesh sieve, the sieved powder is placed in a muffle furnace for calcination at 800-1000 DEG C for 3-6 hours to obtain a magnesia-aluminum spinel carrier. 4 . The NiO/MgAl ₂ O ₄ catalyst according to claim 3 , wherein the ethanol mass fraction of the ethanol aqueous solution is 0-50%. 5 . 5. A NiO/MgAl ₂ O ₄ catalyst according to claim 3, wherein the precipitating agent in step 2 is selected from Na ₂ CO ₃ , (NH ₄ ) ₂ CO ₃ , NaOH, and KOH. one or a mixture of several. 6. A preparation method of NiO/MgAl ₂ O ₄ catalyst as claimed in claim 1, characterized in that, the carrier powder is mixed with the nickel salt powder, placed in a ball-milling tank, grinding beads are added, ground is carried out, and sieved , calcination to obtain NiO/MgAl ₂ O ₄ catalyst. 7 . The preparation method of NiO/MgAl ₂ O ₄ catalyst according to claim 6 , wherein the grinding beads are 95 zirconium beads with a diameter of 2 to 10 mm, and the ball-to-material ratio is the ratio of the mass of the grinding beads to the material. 8 . The ratio is 1:1～6:1; The grinding process is to fix the ball mill jar on the turntable of the planetary ball mill, set the rotation speed to 300-800rpm and the rotation mode to alternate directions for 0-30min, and then mill the ball for 2-8h; The sieving is to pass through a 80-100 mesh sieve, and the roasting is to place the sieved powder in a tube furnace at 600-800 ℃ for 3-6 hours. 8. the preparation method of NiO/MgAl ₂ O ₄ catalyst according to claim 6, is characterized in that, described nickel salt is hexahydrate nickel nitrate, tetrahydrate nickel acetate, dihydrate nickel formate, dihydrate nickel oxalate, One or several mixtures of nickel citrate hydrate. 9. the preparation method of NiO/MgAl ₂ O ₄ catalyst according to claim 6, is characterized in that, on the basis of main active component Ni, can also add other components during ball milling, and other components include Fe, Mn, Ce , La, Zr or Cu precursors are used as cocatalysts. 10. The application of the NiO/MgAl _{2 O 4 catalyst according to claim 1, wherein the NiO/MgAl 2 O 4 catalyst is} used for the catalytic combustion of low-concentration methane or volatile organic gas, and the hydrogenation of organic matter Or reforming hydrogen.

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