Magnesium-aluminum composite oxide supported nickel catalyst as well as preparation method and application thereof

Abstract

The invention discloses a magnesium-aluminum composite oxide loaded nickel catalyst and a preparation method and application thereof, and the preparation method specifically comprises the following steps: (1) dissolving magnesium salt and aluminum salt in water, stirring, adding urea, drying, centrifuging, re-drying, grinding and roasting to obtain a magnesium-aluminum composite oxide; and (2) dissolving nickel salt in water, adding the magnesium-aluminum composite oxide and sodium carbonate, stirring, aging, centrifuging, drying and roasting to obtain the catalyst. The magnesium-aluminum composite oxide loaded nickel catalyst disclosed by the invention is simple in preparation method, good in catalytic performance and recyclable, not only can be used for preparing hydrogen by thermally catalyzing methane reforming, but also can be directly used for adsorbing-photodegrading heavy metal pollutants after being inactivated, and can be used as a photocatalyst for removing hexavalent chromium in water.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and more particularly to a magnesium-aluminum composite oxide supported nickel catalyst, its preparation method and application. Background Art

[0002] As a clean energy source, hydrogen is crucial for reducing greenhouse gas emissions and achieving an energy structure transformation. The development of a hydrogen economy is based on the production of hydrogen. Methane (CH4), which is the main component of natural gas and biogas, can be used to produce high-calorie hydrogen, which is of great significance for carbon reduction and environmental protection. Catalytic methane reforming technology is a potential method for producing low-carbon hydrogen, which can generate hydrogen and solid carbon without directly producing carbon dioxide (CO2). This method is a low-carbon hydrogen production method with advantages such as high economy and easy separation of products.

[0003] Currently, in terms of hydrogen production capacity, Ni-based catalysts are usually used as catalysts for catalytic methane reforming due to their excellent catalytic conversion activity. However, during the high-temperature thermal catalytic reaction process, the active site Ni metal will gradually agglomerate, resulting in a decrease in activity. For the dispersion of active sites, a carrier can usually be added. By loading on the carrier, a large surface area can be promoted, thereby providing more active sites, making it easier for reactant molecules to contact the catalyst surface, and thus improving the reaction rate and efficiency. By regulating the loading amount of the active site Ni, the interaction between the metal and the carrier can be coordinated, thereby affecting the state of the Ni active species in the thermal catalytic reaction, and further realizing the regulation of the activity of the methane conversion to hydrogen reaction and the type of enriched carbon species. Since the by-product carbon is enriched on the surface of the catalyst Ni active site during the hydrogen production process, the catalyst will eventually be deactivated. In this regard, for the deactivation caused by the enrichment of solid carbon on the catalyst surface, pyrometallurgy and hydrometallurgy recovery treatments are usually used, which will inevitably cause an additional burden on the environment.

[0004] On the other hand, hexavalent chromium is a highly toxic heavy metal that poses a serious threat to the environment and human health. In terms of water treatment for degrading pollutants, photocatalytic technology can effectively degrade hexavalent chromium and is a green and environmentally friendly treatment method. The catalyst deactivated during the thermal catalytic hydrogen production process can be reused as a photocatalyst for photocatalytic degradation of hexavalent chromium. Considering that nanocarbon materials are widely used in the field of photocatalysis due to their electron-carrying ability, and photocatalytic water treatment pollutant technology, as a green, environmentally friendly, economical and efficient method, has gradually become a research hotspot for removing hexavalent chromium due to its advantages such as low energy consumption, no secondary pollution, and utilization of solar energy. In addition, by regulating the components of the hydrogen production catalyst, a catalyst for synthesizing enriched carbon nanotubes can be obtained while producing hydrogen. Since the gas-solid reaction does not contain other pollutants, the produced catalyst for synthesizing enriched carbon nanotubes can be directly used as an adsorption-photodegradation hexavalent chromium catalyst without additional treatment or purification steps.

[0005] Therefore, in view of the dual problems of producing new energy and degrading pollutants, how to develop a catalyst that can be used simultaneously for thermocatalytic methane reforming to produce hydrogen and adsorptive-photodegradation of heavy metal pollutants is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a nickel catalyst supported on magnesium-aluminum composite oxide, its preparation method and application, to achieve the dual environmental protection significance of energy production and pollution reduction and to solve the deficiencies in the prior art.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A preparation method of a nickel catalyst supported on magnesium-aluminum composite oxide specifically includes the following steps:

[0009] (1) Hydrothermal method: Dissolve magnesium salt and aluminum salt in water, stir, add urea, dry, centrifuge, dry again, grind, and calcine to obtain magnesium-aluminum composite oxide;

[0010] (2) Deposition precipitation method: Dissolve nickel salt in water, add magnesium-aluminum composite oxide and sodium carbonate, stir, age, centrifuge, dry, and calcine to obtain the nickel catalyst supported on magnesium-aluminum composite oxide.

[0011] Further, in the above step (1), the magnesium salt is at least one of magnesium nitrate, magnesium chloride, and magnesium sulfate; the aluminum salt is at least one of aluminum nitrate, aluminum chloride, and aluminum sulfate; the molar ratio of the magnesium salt to the aluminum salt is 3:1.

[0012] The beneficial effect of adopting the above is that the nitrates (magnesium nitrate or aluminum nitrate) selected in the present invention have strong oxidizing property, high solubility, and good thermal decomposition characteristics, which are suitable for oxidation reactions and the preparation of metal oxides; the chlorides (magnesium chloride or aluminum chloride) selected in the present invention have high solubility, strong reaction activity, and are easy to purify, which are suitable for high concentration and high reaction rate requirements; the sulfates (magnesium sulfate or aluminum sulfate) selected in the present invention have high stability, moderate solubility, and low cost, which are suitable for stable reaction conditions and large-scale production.

[0013] Further, in the above step (1), the molar amount of urea is 1.5 times the total molar amount of metal ions in the magnesium salt and the aluminum salt.

[0014] The beneficial effect of adopting the above is that urea, as a slow-release precipitating agent, can effectively control the precipitation process in the hydrothermal method, improve the product purity, uniform dispersion, and regulate the morphology and particle size, with simple operation and suitable for wide application.

[0015] Further, in the above step (1), the drying equipment is an oven, the temperature is 120 °C, and the time is 24 h; centrifugation is performed by alternately centrifuging with absolute ethanol and ultrapure water; the equipment for re-drying is an oven, the temperature is 70 °C, and the time is 12 h; the roasting equipment is a muffle furnace, the heating rate is 2 °C / min, heated to 700 °C, and kept at a constant temperature for 4 h.

[0016] The beneficial effect of the above further step is that high-temperature roasting of the magnesium-aluminum hydrotalcite forms a magnesium-aluminum composite oxide, which can effectively improve its thermal stability, specific surface area, surface basicity, and catalytic activity. At the same time, it has the environmental-friendly characteristics of being non-toxic and harmless, and is suitable for fields such as catalysis, adsorption, and environmental protection.

[0017] Further, in the above step (2), the nickel salt is at least one of nickel nitrate, nickel chloride, and nickel sulfate; the mass of nickel element in the nickel salt is 15%-45% of the mass of the magnesium-aluminum composite oxide-supported nickel catalyst, preferably 15%, 25%, 35%, and 45%.

[0018] The beneficial effect of the above further step is that the nickel nitrate selected in the present invention has strong oxidizing property, high solubility, and good thermal decomposition characteristics, and is suitable for oxidation reactions and the preparation of metal oxides; the nickel chloride selected in the present invention has high solubility, strong reaction activity, and is easy to purify, and is suitable for the requirements of high concentration and high reaction rate; the nickel sulfate selected in the present invention has high stability, moderate solubility, and low cost, and is suitable for stable reaction conditions and large-scale production.

[0019] Further, in the above step (2), the sodium carbonate is anhydrous sodium carbonate and / or sodium carbonate monohydrate; the sodium carbonate is added until the pH of the system is 9.0-9.5.

[0020] The beneficial effect of the above further step is that sodium carbonate, as a precipitant, has strong solubility, is convenient for adjusting the pH, can promote the precipitation of nickel salt, is convenient for the filtration process of the precipitate, and has the advantages of environmental friendliness, low cost, simple operation, and few product impurities.

[0021] Further, in the above step (2), the stirring time is 4 h; the aging time is 12 h; centrifugation is performed by alternately centrifuging with absolute ethanol and ultrapure water; the roasting equipment is a muffle furnace, the heating rate is 2 °C / min, heated to 700 °C, and kept at a constant temperature for 4 h.

[0022] The beneficial effect of the above further step is that the present invention calcines the product prepared by the deposition precipitation method, which can promote the formation of strong interactions between nickel species and the carrier, improve the stability of the catalyst, prevent sintering and loss; during the calcination process, it promotes the nickel species on the surface of the carrier, increasing the active sites; calcination can remove volatile impurities and improve the purity of the catalyst.

[0023] The present invention also claims protection for a nickel catalyst supported on magnesium-aluminum composite oxide prepared by the above preparation method.

[0024] The present invention also claims protection for the application of a nickel catalyst supported on magnesium-aluminum composite oxide prepared by the above preparation method in the thermal catalytic reforming of methane to hydrogen.

[0025] Furthermore, the above application specifically is: carrying out thermal catalytic conversion of methane to hydrogen in a small fixed bed. Specifically, it includes the following steps:

[0026] (1) Loading the prepared nickel catalyst supported on magnesium-aluminum composite metal oxide into a quartz tube;

[0027] (2) Passing 5 vol% methane as the raw material into the quartz tube and heating it using a tube furnace;

[0028] (3) Collecting and analyzing the tail gas generated after heating.

[0029] The present invention also claims protection for the application of a nickel catalyst supported on magnesium-aluminum composite oxide prepared by the above preparation method in the adsorption-photodegradation of heavy metal pollutants.

[0030] Furthermore, the above application specifically is: directly using the waste catalyst after thermal catalytic hydrogen production as a photocatalyst for the adsorption-photodegradation of hexavalent chromium. Specifically, it includes the following steps:

[0031] Mixing the waste catalyst after thermal catalytic hydrogen production with an aqueous solution of hexavalent chromium with a concentration of 20 mg / L according to a solid-liquid ratio of 1:5000, centrifuging after reaching adsorption equilibrium, filtering with a 0.2 - 0.45 μm filter membrane, and then collecting and analyzing to determine the adsorption performance of the catalyst for hexavalent chromium in the aqueous solution.

[0032] Through the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. The enriched carbon nanotube material generated by thermal catalytic hydrogen production has good photocatalytic activity as an adsorption-photodegradation catalyst for hexavalent chromium. The presence of carbon nanotubes can make the material more effectively reduce the load rate of photo-generated carriers. This is because carbon nanotubes have excellent electron transport performance and a large specific surface area, which can effectively capture and transport photo-generated electrons, realizing the effective separation of photo-generated electron-hole pairs, and then realizing an efficient photocatalytic effect. It is important to achieve environmental purification and energy conversion through technological innovation, especially in the fields of hydrogen energy development and water treatment. The present invention converts the by-product generated in the process of thermal catalytic hydrogen production into a photocatalyst, realizing the reuse of waste and the effective removal of environmental pollutants. It not only improves the energy utilization efficiency but also reduces environmental pollution, and realizes the reuse of solid waste, reflecting the concept of sustainable development.

[0034] 2. In view of the limitations of the prior art, the present invention provides a new co-production strategy. By regulating the interaction between the metal and the support, this strategy can efficiently convert methane to hydrogen during the thermocatalytic conversion process. Meanwhile, carbon nanotube species are enriched on the catalyst surface, and the deactivated thermocatalyst due to carbon species enrichment is used as an efficient adsorptive photocatalyst. Utilizing its characteristics in specific surface area, band gap, light absorption, etc., its photocatalytic activity is significantly enhanced for the adsorption and removal of hexavalent chromium in water pollution.

[0035] 3. The nickel catalyst supported on magnesium-aluminum composite oxide of the present invention is simple to prepare, low in cost, good in catalytic performance, and recyclable. It can not only be used for thermocatalytic methane reforming to produce hydrogen, but also directly be used for adsorbing-photodegrading heavy metal pollutants after deactivation, and remove hexavalent chromium in water as a photocatalyst.

[0036] 4. The present invention provides a method for co-producing hydrogen with carbon nanotubes that is simple to prepare and low in cost. The prepared carbon nanotubes have a good tubular structure.

[0037] 5. The present invention coordinates the interaction between the metal and the support by controlling the loading amount, achieving high-efficiency methane conversion rate and hydrogen production rate.

[0038] 6. The present invention directly re-uses the waste catalyst after thermocatalytic hydrogen production as an adsorptive photocatalyst for removing hexavalent chromium, providing a new way of environmental resource recycling. At the same time, the specific surface area and abundant active sites of this catalyst can effectively promote the photocatalytic efficiency.

[0039] 7. The preparation method of the present invention does not involve highly toxic and highly harmful substances throughout the process, and is simple in operation, mild in conditions, and easy for industrial production. Meanwhile, it provides a feasible strategy for low-carbon hydrogen production and direct resource conversion of waste catalysts, and also solves the environmental risks related to the secondary pollution of waste catalyst recycling and treatment.

[0040] 8. The present invention combines thermocatalytic hydrogen production and photocatalytic degradation of pollutants, achieving an environmentally friendly dual response of energy production and pollution reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Instantaneous methane conversion rate of the nickel catalyst supported on magnesium-aluminum composite oxide for thermocatalytic conversion of methane to hydrogen in Examples 1 - 4;

[0042] Figure 2 Instantaneous hydrogen production rate of the nickel catalyst supported on magnesium-aluminum composite oxide for thermocatalytic conversion of methane to hydrogen in Examples 1 - 4;

[0043] Figure 3 X-ray diffraction pattern (XRD) of the deactivated catalyst after the thermocatalytic conversion of methane to hydrogen by the nickel catalyst supported on magnesium-aluminum composite oxide in Examples 1 - 4;

[0044] Figure 4 For the degradation efficiency of the deactivated catalyst used in the photocatalysis of hexavalent chromium after the thermocatalytic conversion of methane to hydrogen over the magnesium-aluminum composite oxide supported nickel catalyst in Examples 1-4;

[0045] Figure 5 For the specific surface area (BET) of the deactivated catalyst after the thermocatalytic conversion of methane to hydrogen over the magnesium-aluminum composite oxide supported nickel catalyst in Example 2;

[0046] Figure 6 For the high-resolution transmission electron microscopy (TEM) image of the deactivated catalyst after the thermocatalytic conversion of methane to hydrogen over the magnesium-aluminum composite oxide supported nickel catalyst in Example 2. Specific implementation manners

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0048] Example 1

[0049] A preparation method of a magnesium-aluminum composite oxide supported nickel catalyst specifically includes the following steps:

[0050] (1) First, dissolve 0.03 mol of magnesium nitrate and 0.01 mol of aluminum nitrate in deionized water, stir magnetically, slowly dropwise add an aqueous solution of 0.06 mol of urea, stir for 1 h, then pour it into a high-pressure reaction kettle, and place it in a drying oven at 120 °C for 24 h. Then, alternately centrifuge with absolute ethanol and ultrapure water, place the filter cake in a drying oven at 70 °C for 12 h, grind it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain a magnesium-aluminum composite oxide;

[0051] (2) First, dissolve nickel salt in deionized water. The mass of nickel element in nickel nitrate is 15% of the mass of the magnesium-aluminum composite oxide supported nickel catalyst. Then, add the magnesium-aluminum composite oxide, and while stirring, titrate an aqueous solution of anhydrous sodium carbonate to the system pH of 9.0, stir for 4 h, age for 12 h, alternately centrifuge with absolute ethanol and ultrapure water, dry it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain the magnesium-aluminum composite oxide supported nickel catalyst.

[0052] Example 2

[0053] A preparation method of a magnesium-aluminum composite oxide supported nickel catalyst specifically includes the following steps:

[0054] (1) First, dissolve 0.03 mol of magnesium nitrate and 0.01 mol of aluminum nitrate in deionized water, stir magnetically, slowly add dropwise an aqueous solution of 0.06 mol of urea, after stirring for 1 h, pour it into a high-pressure reactor, and place it in a drying oven at 120 °C for drying for 24 h. Then, alternately centrifuge with absolute ethanol and ultrapure water, place the filter cake in a drying oven at 70 °C for drying for 12 h, grind it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain a magnesium-aluminum composite oxide;

[0055] (2) First, dissolve the nickel salt in deionized water. The mass of nickel element in nickel nitrate is 25% of the mass of the nickel-loaded magnesium-aluminum composite oxide catalyst. Then, add the magnesium-aluminum composite oxide, and while stirring, titrate an aqueous solution of anhydrous sodium carbonate to the system until the pH is 9.0, stir for 4 h, age for 12 h, alternately centrifuge with absolute ethanol and ultrapure water, dry it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain the nickel-loaded magnesium-aluminum composite oxide catalyst.

[0056] Example 3

[0057] A preparation method of a nickel-loaded magnesium-aluminum composite oxide catalyst specifically includes the following steps:

[0058] (1) First, dissolve 0.03 mol of magnesium nitrate and 0.01 mol of aluminum nitrate in deionized water, stir magnetically, slowly add dropwise an aqueous solution of 0.06 mol of urea, after stirring for 1 h, pour it into a high-pressure reactor, and place it in a drying oven at 120 °C for drying for 24 h. Then, alternately centrifuge with absolute ethanol and ultrapure water, place the filter cake in a drying oven at 70 °C for drying for 12 h, grind it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain a magnesium-aluminum composite oxide;

[0059] (2) First, dissolve the nickel salt in deionized water. The mass of nickel element in nickel nitrate is 35% of the mass of the nickel-loaded magnesium-aluminum composite oxide catalyst. Then, add the magnesium-aluminum composite oxide, and while stirring, titrate an aqueous solution of anhydrous sodium carbonate to the system until the pH is 9.0, stir for 4 h, age for 12 h, alternately centrifuge with absolute ethanol and ultrapure water, dry it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain the nickel-loaded magnesium-aluminum composite oxide catalyst.

[0060] Example 4

[0061] A preparation method of a nickel-loaded magnesium-aluminum composite oxide catalyst specifically includes the following steps:

[0062] (1) First, dissolve 0.03 mol of magnesium nitrate and 0.01 mol of aluminum nitrate in deionized water, stir magnetically, and slowly add dropwise an aqueous solution of 0.06 mol of urea. After stirring for 1 h, pour it into a high-pressure reactor and place it in a drying oven at 120 °C for 24 h. Then, alternately centrifuge with absolute ethanol and ultrapure water, place the filter cake in a drying oven at 70 °C for 12 h, grind it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain a magnesium-aluminum composite oxide;

[0063] (2) First, dissolve the nickel salt in deionized water. The mass of nickel element in nickel nitrate is 45% of the mass of the nickel-loaded catalyst on the magnesium-aluminum composite oxide. Then, add the magnesium-aluminum composite oxide, and while stirring, titrate an aqueous solution of anhydrous sodium carbonate dropwise until the pH of the system is 9.0. Stir for 4 h, age for 12 h, alternately centrifuge with absolute ethanol and ultrapure water, dry it, and finally place it in a muffle furnace and calcine it at a heating rate of 2 °C / min to 700 °C for 4 h to obtain the nickel-loaded catalyst on the magnesium-aluminum composite oxide.

[0064] Production capacity and pollution reduction performance test

[0065] 1. In terms of production capacity: Thermal catalytic conversion of methane to hydrogen test

[0066] Test in a small fixed bed. Respectively place 0.3 g of the nickel-loaded catalyst on the magnesium-aluminum composite oxide prepared in Examples 1-4 in a quartz tube and set the test procedure in a tube furnace. First, use high-purity N2 as an inert protective gas to pretreat the catalyst, gradually heat it from room temperature to 700 °C at a heating rate of 10 °C / min. Then, switch the gas to 10% H2 for reduction treatment for 1 h. After that, purge with high-purity N2 and then introduce 5% CH4 / N2 to react for 100 min. Quantify the products and reactants by combining a gas chromatograph and a flue gas analyzer. The results are as Figure 1-2 shown.

[0067] It can be seen from Figure 1-2 the above that the sample loaded with 25% nickel in Example 2 has the best thermal catalytic activity and excellent hydrogen production performance.

[0068] 2. In terms of pollution reduction: Adsorption-photodegradation of heavy metal pollutants test

[0069] Take out the deactivated catalyst after the thermal catalytic conversion of methane to hydrogen reaction of the nickel-loaded catalyst on the magnesium-aluminum composite oxide in Examples 1-4 in the above "Thermal catalytic conversion of methane to hydrogen test", grind it evenly into powder with an agate mortar, encapsulate and store it, and conduct photocatalytic performance detection.

[0070] The photocatalytic degradation performance test of hexavalent chromium is as follows: After the deactivated catalysts (20 mg) obtained from the thermal catalytic conversion of methane to hydrogen using the magnesium-aluminum composite oxide supported nickel catalysts of Examples 1-4 were respectively added to 50 mL of aqueous solution, where the hexavalent chromium source was a solution of potassium dichromate with a concentration of 20 mg / L. In a dark environment, magnetic stirring was carried out for 30 min, and samples were taken at intervals for absorbance measurement. Then, a CEL-HXF300 xenon lamp was turned on as the light source for the photoreaction. A cooling water recirculation system was used to continuously stir the reaction mixture with a magnetic stirrer to maintain room temperature conditions. Under an ultraviolet-visible spectrophotometer, the hexavalent chromium concentration was recorded by the diphenylcarbazide spectrophotometric method. The results are as Figures 3-6 shown.

[0071] It can be Figure 3 seen that the sample of Example 2 loaded with 25% nickel has the most carbon deposition.

[0072] It can be Figure 4 seen that the sample of Example 2 loaded with 25% nickel has the best degradation efficiency.

[0073] It can be Figures 5-6 seen that the larger specific surface area of the sample of Example 2 loaded with 25% nickel and the carbon nanotubes enriched on the catalyst surface promote the contact area between the reactants and the catalyst, increase the number of active sites, and thus improve the pollution reduction efficiency.

[0074] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst, characterized in that: The specific steps include: (1) dissolving magnesium salt and aluminum salt in water, stirring, adding urea, drying, centrifuging, drying again, grinding, and roasting to obtain a magnesium-aluminum composite oxide; (2) dissolving nickel salt in water, adding magnesium aluminum composite oxide and sodium carbonate, stirring, aging, centrifuging, drying, and calcining to obtain the magnesium aluminum composite oxide-supported nickel catalyst.

2. The method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst according to claim 1, characterized in that: In step (1), the magnesium salt is at least one of magnesium nitrate, magnesium chloride and magnesium sulfate; the aluminum salt is at least one of aluminum nitrate, aluminum chloride and aluminum sulfate; and the molar ratio of the magnesium salt to the aluminum salt is 3:

1.

3. The method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst according to claim 1, characterized in that: In step (1), the molar amount of urea is 1.5 times the total molar amount of metal ions in the magnesium salt and the aluminum salt.

4. The method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst according to claim 1, characterized in that: In step (1), the drying device is a drying oven, the temperature is 120°C, and the time is 24 hours; the centrifugation is an alternating centrifugation treatment with anhydrous ethanol and ultrapure water; the re-drying device is a drying oven, the temperature is 70°C, and the time is 12 hours; the roasting device is a muffle furnace, the heating rate is 2°C / min, the temperature is raised to 700°C, and the temperature is kept constant for 4 hours.

5. The method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst according to claim 1, characterized in that: In step (2), the nickel salt is at least one of nickel nitrate, nickel chloride and nickel sulfate; the mass of the nickel element in the nickel salt is 15%-45% of the mass of the magnesium-aluminum composite oxide-supported nickel catalyst.

6. The method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst according to claim 1, characterized in that: In step (2), the sodium carbonate is anhydrous sodium carbonate and / or sodium carbonate monohydrate; the sodium carbonate is added to the system at a pH of 9.0-9.

5.

7. The method for preparing a magnesium-aluminum composite oxide-supported nickel catalyst according to claim 1, characterized in that: In step (2), the stirring time is 4 hours; the aging time is 12 hours; the centrifugation is performed by alternating centrifugation with anhydrous ethanol and ultrapure water; the roasting equipment is a muffle furnace, the heating rate is 2°C / min, the temperature is raised to 700°C, and the temperature is maintained for 4 hours.

8. A magnesium-aluminum composite oxide-supported nickel catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of a magnesium-aluminum composite oxide-supported nickel catalyst prepared by the preparation method according to any one of claims 1 to 7 in thermal catalytic methane reforming to produce hydrogen.

10. Use of a magnesium-aluminum composite oxide-supported nickel catalyst prepared by the preparation method according to any one of claims 1 to 7 in the adsorption-photodegradation of heavy metal pollutants.

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