Ni-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to a Ni-based catalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalysts. The general formula of the Ni-based catalyst is Ni / MTiO2, MTiO2 is a titanium oxide carrier modified by M metal, and the M metal is selected from at least one of Mn, Fe, Co, Zn and Cu; the mass fraction of Ni in the Ni / MTiO2 is 5%-30%; the mass fraction of the metal M in the modified titanium oxide carrier is 1-20%. The preparation method comprises the following steps: firstly preparing an M metal modified titanium dioxide carrier, then loading an active component Ni on the carrier, and then carrying out activating treatment to obtain the Ni-based catalyst. The catalyst provided by the invention can realize high-efficiency methane cracking hydrogen production at a low temperature, the H2 yield is high, side reactions are few, and the preparation method provided by the invention is simple and easy to implement and low in cost, and shows a good application prospect.

Description

Technical Field

[0001] The invention relates to a Ni-based catalyst and a preparation method and application thereof, belonging to the technical field of photocatalysts. Background Art

[0002] As a type of green and zero-pollution energy, hydrogen energy occupies an important position in the chemical industry and future energy structure. At present, large-scale hydrogen production is mainly achieved through reforming reaction technology of carbon-containing resources such as alkanes. This process not only consumes a lot of energy, but also produces a lot of carbon dioxide. This is contrary to the current global carbon emission reduction and sustainable development goals. The development of hydrogen production technology driven by renewable light sources not only provides a clean energy carrier, but also solves the problem of energy storage. It has important strategic significance in energy transformation and reducing greenhouse gas emissions.

[0003] Sakae Takenaka et al.'s paper Methane decomposition into hydrogen and carbon nanofibers over supported Pd–Ni catalysts discloses a supported Ni catalyst, with the support selected from SiO2, TiO2, etc., and a second metal Pd added. The methane cracking temperature is 873K (600°C), and the catalyst is deactivated 4 hours after the reaction. Pd is a precious metal, and the catalyst deactivates quickly, so the cost is relatively high; the reaction temperature is 600°C, and there is still room for reduction.

[0004] Xiamen University's degree thesis: Preparation, characterization and photocatalytic reduction and oxidation performance of carbon nanotube and titanium dioxide composite catalysts disclosed a Ni-based catalyst composed of 65% Ni, 10% Cu, and 25% SiO2. Its methane conversion rate was 88.74%. The catalyst remained active for a long time, but the reaction temperature was too high, at 650°C.

[0005] Chinese patent CN114591130A discloses a method for photocatalytic methane water phase coupling, wherein the catalyst carrier is TiO2, and the loaded metal is one or more of silver, gold, copper, platinum, palladium, ruthenium, rhodium, and zinc, preferably silver, gold, copper, platinum, and palladium. The catalyst catalyzes the cracking of methane to produce hydrogen and ethylene, and the reaction is photocatalytic. The hydrogen generation rate is 1726μmol·g -1 ·h -1 , the hydrogen production rate is low and the metals used are mostly precious metals, so the cost is high.

[0006] The high bond energy of the CH bond in the methane molecule makes it difficult to activate and break it, which usually requires high temperatures to be effective. This not only limits the reaction rate of direct conversion of methane to hydrogen, but also greatly increases the energy consumption and equipment investment of the overall technology, limiting the commercial application of direct catalytic conversion of methane. Therefore, it is urgent to provide a technical solution to address the above-mentioned deficiencies in the existing technology. Summary of the invention

[0007] In a first aspect, the present invention provides a Ni-based catalyst having the general formula of Ni / MTiO2, wherein MTiO2 is a titanium oxide carrier modified by M metal;

[0008] The M metal is selected from at least one of Mn, Fe, Co, Zn and Cu;

[0009] Preferably, the M metal is selected from at least one of Mn, Fe, Co and Zn;

[0010] The mass fraction of Ni in Ni / MTiO2 is 5%-30%;

[0011] Preferably, the mass fraction of Ni in Ni / MTiO2 is 20%-30%;

[0012] The mass fraction of the M metal in the modified titanium oxide carrier is 0.1-20%;

[0013] Preferably, the mass fraction of the M metal in the modified titanium oxide carrier is 8-20%;

[0014] The titanium oxide is at least one of rutile type, anatase type and P25 mixed type.

[0015] In a second aspect, the present invention provides a method for preparing a Ni-based catalyst, comprising the following steps:

[0016] S1, dissolving the M metal salt in water, adding titanium oxide powder to obtain solution L1;

[0017] S2, adding alkali solution to solution L1, aging after precipitation is completed, and obtaining mixed solution L2;

[0018] S3, filtering, washing, drying and calcining the mixed solution L2 to obtain a titanium oxide carrier modified with metal M;

[0019] S4, dissolving Ni salt in water to obtain a Ni salt solution, adding a sacrificial agent and the titanium oxide carrier modified with metal M obtained in step S3, and performing ultrasonication to obtain a suspension;

[0020] S5, placing the suspension obtained in step S4 in a reactor for photodeposition reaction, and then filtering, drying, calcining, reducing and passivating to obtain the Ni-based catalyst;

[0021] The sacrificial agent is at least one of methanol, ethanol, isopropanol and butanol;

[0022] The M metal salt in step S1 is at least one of the chloride, nitrate, sulfate and acetate of the M metal;

[0023] The molar concentration of total M metal ions in the M metal salt solution in step S1 is 0.1-2 mol / L;

[0024] The concentration of the alkali solution in step S2 is 0.1-2 mol / L;

[0025] The alkali solution in step S2 is at least one of potassium hydroxide or sodium hydroxide;

[0026] The precipitation in step S2 is completed at a pH value of 8-12;

[0027] The aging temperature in step S2 is 40-200°C and the time is 0.5-20h;

[0028] The drying condition in step S3 is 60°C-200°C, and the drying time is 2-20h;

[0029] The calcination temperature in step S3 is 400-500°C and the calcination time is 2-4h;

[0030] The Ni salt in step S4 is at least one of chloride, nitrate, sulfate and acetate;

[0031] The concentration of the Ni salt solution in step S4 is 0.1-1 mol / L;

[0032] The mass ratio of the amount of the sacrificial agent added in step S4 to the Ni salt solution is 0.1-0.2:1;

[0033] The conditions of the photodeposition reaction in step S5 are: light irradiation reaction at 20-30°C;

[0034] Preferably, the light source used in the reaction is at least one of a xenon lamp, a high pressure mercury lamp or a black light lamp;

[0035] In step S5, the drying temperature is 60°C-200°C, and the drying time is 2h-20h; the calcination temperature is 300-600°C, and the calcination time is 2-10h;

[0036] The reduction conditions in step S5 are as follows: in a reducing atmosphere, at a temperature of 400° C. to 500° C., for a time of 2 h to 4 h;

[0037] Specifically, the reducing atmosphere is hydrogen;

[0038] The passivation gas used in step S5 is a mixture of O2 and Ar, and the passivation time is 0.5-2h;

[0039] Specifically, the volume concentration of O2 is 0.5%.

[0040] In a third aspect, the present invention provides a Ni-based catalyst for use in direct cracking of methane to produce hydrogen.

[0041] In a fourth aspect, the present invention provides a method for preparing hydrogen, using a mixed gas containing CH4 as a raw material, using the above-mentioned Ni-based catalyst or the Ni-based catalyst prepared by the above-mentioned preparation method for photocatalytic cracking to obtain;

[0042] Specifically, the light source in the photocatalysis is sunlight;

[0043] Preferably, the light source in the photocatalysis is a combination of two convex lenses for focusing light;

[0044] Preferably, a 200W full-spectrum xenon lamp can be added as the light source in the photocatalysis.

[0045] Preferably, the mixed gas is a mixed gas of CH4 and N2, the volume ratio is 9:1, and the flow rate of the raw gas is 10 mL / min;

[0046] A Ni-based catalyst and a preparation method and application thereof of the present invention have the following beneficial effects:

[0047] (1) The present invention improves the absorption efficiency of solar energy by regulating the interaction between active sites and carriers, thereby achieving efficient utilization of solar energy by methane;

[0048] (2) The present invention produces hydrogen with high activity and high conversion rate under relatively mild conditions, thereby solving the problem of the difficulty in utilizing light energy and the high demand for thermal energy in the direct cracking reaction of methane to produce hydrogen;

[0049] (3) The present invention has almost no side reactions and has good economic efficiency;

[0050] (4) The preparation method of the present invention is simple and can be produced on a large scale. DETAILED DESCRIPTION

[0051] To better illustrate this patent, the following examples are listed. The following examples are intended to enable the industry personnel to understand the present invention in more detail, or to make some non-essential improvements and adjustments based on the content of the present invention. However, the scope of the present invention is not limited by these examples.

[0052] 1. Examples and Comparative Examples

[0053] Example 1

[0054] According to the mass percentage of metal Mn in the modified carrier of 20%, a manganese nitrate solution with a concentration of 1 mol / L is prepared, and a calculated amount of rutile TiO2 is added. A 1 mol / L sodium hydroxide aqueous solution is added dropwise to the vigorously stirred metal salt solution until the pH value of the solution reaches 9. The precipitate is then aged at 80°C for 12 hours. The resulting precipitate is thoroughly washed with deionized water until the pH value of the washing liquid reaches neutral. The filter cake is then dried at 80°C for 6 hours and calcined in a muffle furnace at 450°C for 3 hours. The resulting solid is ground to obtain a titanium oxide carrier modified with metal Mn.

[0055] A nickel nitrate solution with a concentration of 0.5 mol / L was prepared according to the metal Ni accounting for 10% of the weight of the catalyst, and a titanium oxide carrier modified with metal Mn was added. Methanol of 10% of the mass of the solution was added as a sacrificial agent, the mixed solution was fully ultrasonically mixed, and then placed in a photodeposition reactor, and the photodeposition reaction was carried out under a xenon lamp light source. The obtained mixture was centrifuged, filtered and washed 6 times, then dried at 120°C for 10 hours, and calcined in a muffle furnace at 450°C for 5 hours. The obtained solid was reduced in a hydrogen atmosphere at 450°C for 3 hours, and then passivated in a passivation gas with a volume ratio of O2 to Ar2 of 1:99 for 1 hour to obtain a Ni-based catalyst.

[0056] Examples 2-12 and Comparative Examples 1-6

[0057] The material list of Examples 2-12 is shown in Table 1, and the preparation method is the same as that of Example 1.

[0058] Table 1 Materials list of Examples 1-12 and Comparative Examples 1-6

[0059]

[0060]

[0061] 2. Photocatalytic methane direct cracking to produce hydrogen

[0062] The Ni-based catalysts in Examples 1-12 of the present invention and Comparative Examples 1-6 were used in the photocatalytic methane direct cracking hydrogen production reaction, and the performance of the Ni-based catalyst was evaluated. 0.02 g of the Ni-based catalyst was weighed, the raw gas was selected as CH4 / N2=9 (volume ratio), the flow rate of the raw gas was 10 mL / min, the light source was provided by a combination of two convex lenses to focus sunlight and a 200 W full-spectrum xenon lamp, the reaction time was 2 h, the reaction pressure was normal pressure, and the performance results are shown in Table 2.

[0063] Table 2 Hydrogen yield of Examples 1-12 and Comparative Examples 1-6

[0064]

[0065]

[0066] When the M metal is selected from one of Mn, Fe, Co, Zn, and Cu, the hydrogen yield of Examples 1-12 of the present invention is high. Preferably, when the M metal is selected from Mn, Fe, Co, and Zn, the effect is better, and the maximum can reach 460.1 mmol / gcat / h. When other types of metals are selected, such as Pd in ​​Comparative Example 1, the hydrogen yield is only 198.2 mmol / gcat / h.

[0067] When the mass fraction of Ni in the catalyst is 5%-30%, the hydrogen yield of Examples 1-12 of the present invention is high. Preferably, when the mass fraction of Ni in the catalyst is 20%-30%, the effect is better. When Ni in other mass fraction ranges is selected, such as Comparative Examples 2-3, the hydrogen yield is only 226.6mmol / gcat / h.

[0068] When the mass fraction of M metal in the modified titanium oxide carrier is 0.1-20%, the hydrogen yield of Examples 1-12 of the present invention is high. Preferably, when the mass fraction of M metal in the modified titanium oxide carrier is 8-20%, the effect is better. When M metal in other mass fraction ranges is selected, such as Comparative Examples 4-5, the hydrogen yield is less than 200 mmol / gcat / h.

[0069] The present invention uses TiO2 as a carrier, and the hydrogen yield of Examples 1-12 of the present invention is high. When other types of carriers, such as SiO2 in Comparative Example 6, are used, the hydrogen yield is only 160.2 mmol / gcat / h.

Claims

1. A Ni-based catalyst, characterized in that The general formula is Ni / MTiO2, wherein MTiO2 is a titanium oxide carrier modified by M metal; The M metal is selected from at least one of Mn, Fe, Co, Zn and Cu; The mass fraction of Ni in Ni / MTiO2 is 5%-30%; The mass fraction of the M metal in the modified titanium oxide carrier is 0.1-20%.

2. The Ni-based catalyst according to claim 1, characterized in that The titanium oxide is at least one of rutile type, anatase type and P25 mixed type.

3. A method for preparing a Ni-based catalyst as claimed in any one of claims 1 to 2, characterized in that: The steps include: S1, dissolving the M metal salt in water, adding titanium oxide powder to obtain solution L1; S2, adding alkali solution to solution L1, aging after precipitation is completed, and obtaining mixed solution L2; S3, filtering, washing, drying and calcining the mixed solution L2 to obtain a titanium oxide carrier modified with metal M; S4, dissolving Ni salt in water to obtain a Ni salt solution, adding a sacrificial agent and the titanium oxide carrier modified with metal M obtained in step S3, and performing ultrasonication to obtain a suspension; S5, placing the suspension obtained in step S4 in a reactor for photodeposition reaction, and then filtering, drying, calcining, reducing and passivating to obtain the Ni-based catalyst; The sacrificial agent is at least one of methanol, ethanol, isopropanol and butanol.

4. The preparation method according to claim 3, characterized in that: The M metal salt in step S1 is at least one of the chloride, nitrate, sulfate and acetate of the M metal.

5. The preparation method according to claim 3, characterized in that: The alkali solution in step S2 is at least one of potassium hydroxide or sodium hydroxide; The precipitation in step S2 is completed at a pH value of 8-12; The aging temperature in step S2 is 40-200° C. and the aging time is 0.5-20 h.

6. The preparation method according to claim 3, characterized in that: The drying condition in step S3 is 60°C-200°C, and the drying time is 2-20h; The calcination temperature in step S3 is 400-500° C. and the calcination time is 2-4 hours.

7. The preparation method according to claim 3, characterized in that: The Ni salt in step S4 is at least one of chloride, nitrate, sulfate and acetate; The concentration of the Ni salt solution in step S4 is 0.1-1 mol / L; The mass ratio of the added amount of the sacrificial agent to the Ni salt solution in step S4 is 0.1-0.2:

1.

8. The preparation method according to claim 3, characterized in that: The conditions of the photodeposition reaction in step S5 are: light irradiation reaction at 20-30° C., reaction time 2-10 h; The light source of the illumination reaction is at least one of a xenon lamp, a high pressure mercury lamp or a black light lamp; The reduction conditions in step S5 are as follows: in a reducing atmosphere, at a temperature of 400° C. to 500° C., for a time of 2 h to 4 h; The passivation gas used in step S5 is a mixed gas of O2 and Ar, and the passivation time is 0.5-2h.

9. Use of the Ni-based catalyst according to any one of claims 1 to 2 or the Ni-based catalyst prepared by the preparation method according to any one of claims 3 to 8 in direct methane cracking to produce hydrogen.

10. A method for preparing hydrogen, characterized in that: The mixed gas containing CH4 is used as a raw material, and the Ni-based catalyst described in any one of claims 1 to 2 or the Ni-based catalyst prepared by the preparation method described in any one of claims 3 to 8 is used for photocatalytic cracking to obtain the product.

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