Preparation method and application of Mn-doped CuAl2O4 spinel

Abstract

The invention provides a preparation method of Mn-doped CuAl2O4 spinel, which comprises the following steps: dissolving a copper salt, an aluminum salt and a manganese salt in ultrapure water, and adding a reducing agent to obtain a precursor solution; heating the precursor solution in a water bath kettle to obtain wet gel; calcining the wet gel in air to obtain precursor powder; inorganic sol and the precursor powder are mixed, ground and roasted in air, and the Mn-doped CuAl2O4 spinel is obtained. The invention also provides application of the spinel, and the spinel is applied to hydrogen production by catalytic alcohol reforming.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production by alcohol reforming, and specifically relates to a preparation method and application of Mn-doped CuAl 2 O 4 spinel. Background Art

[0002] Hydrogen production by alcohol reforming is expected to realize on-line hydrogen supply for hydrogen energy vehicles due to its mild reaction conditions, few by-products and low energy consumption. Copper-based catalysts have the advantages of high activity, high hydrogen selectivity and low price, so they have become the most commonly used catalysts for hydrogen production by alcohol reforming. However, due to the low melting point of copper, the main disadvantage of copper-based catalysts is the rapid deactivation caused by sintering of the active phase. CuAl 2 O 4 is a kind of AB 2 O 4 spinel, which is a cubic lattice oxide composed of Cu 2+ occupying the tetrahedral position and Al 3+ occupying the octahedral position. When using CuAl 2 O 4 spinel to catalyze the hydrogen production reaction by alcohol reforming, nano-sized active copper particles can gradually be released from the spinel structure, resulting in a gradual increase and then a slow decrease in catalytic activity, thus significantly improving the catalytic stability and service life. This characteristic is called slow-release catalysis. However, the acidity of Al 2 O 4 in the CuAl 3+ spinel structure will increase the selectivity of CO in the product and accelerate the carbon deposition rate on the spinel surface, thus having a negative impact on the stability. Therefore, forming composite spinels by doping foreign cations and adding inorganic sols, modifying the surface of copper species, changing the chemical environment of copper species and preventing the agglomeration of homogeneous particles are effective means to further improve the catalytic stability of CuAl 2 O 4 spinel. Summary of the Invention

[0003] The first object of the present invention is to provide an Mn-doped CuAl 2 O 4 spinel with low CO selectivity, low carbon deposition rate and high stability in the catalytic hydrogen production reaction by alcohol reforming.

[0004] The second object of the present invention is to provide a preparation method of the Mn-doped CuAl 2 O 4 spinel.

[0005] The third object of the present invention is to provide an application of the Mn-doped CuAl 2O 4 Applications of spinel.

[0006] To achieve the above object, the present invention adopts the following technical means: A preparation method of Mn-doped CuAl 2 O 4 spinel, characterized by comprising the following steps: Dissolve copper salt, aluminum salt and manganese salt in ultrapure water, then add a reducing agent to obtain a precursor solution; heat the precursor solution in a water bath to obtain a wet gel; calcine the wet gel in air to obtain a precursor powder; mix and grind the inorganic sol with the precursor powder, and calcine in air to obtain Mn-doped CuAl 2 O 4 spinel.

[0007] The copper salt includes at least one of copper nitrate, copper chloride or copper sulfate; The aluminum salt includes at least one of aluminum nitrate, aluminum chloride or aluminum sulfate; The manganese salt includes at least one of manganese nitrate, manganese chloride or manganese sulfate; The reducing agent includes at least one of ethylene glycol, glycine, citric acid, urea, ammonium acetate, carbohydrazide and hydrazine; The molar ratio of the copper salt, aluminum salt, manganese salt to the reducing agent is 0.8~1.6:1.8~2.4:0.1~0.4:4~8; The mass ratio of the inorganic sol to the precursor powder is 0.05~0.15:1; The inorganic sol includes at least one of silica sol, alumina sol or zirconia sol.

[0008] The heating temperature is 60~120°C and the time is 0.5~2h.

[0009] The calcination temperature is 350~450°C and the time is 1~3h.

[0010] The roasting temperature is 700~900°C and the time is 3~6h.

[0011] An application of Mn-doped CuAl 2 O 4 spinel in the catalytic reforming of alcohols for hydrogen production.

[0012] The alcohols include one or more of methanol, ethanol, glycerol or n-butanol.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The spinel provided by the present invention has fine and uniform particles, a large specific surface area and average pore diameter, low acidity, good reduction performance, excellent chemical composition, and good surface chemical state.

[0014] 2. The spinel provided by the present invention has high catalytic activity. After being applied to the reforming of alcohols for hydrogen production, the conversion rate can reach 100%.

[0015] 3. The spinel provided by the present invention has low carbon monoxide selectivity and high catalytic stability in the catalytic reforming of alcohols for hydrogen production. After long-term continuous catalysis, the alcohol conversion rate remains stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Shows the XRD comparison diagrams of the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4.

[0017] Figure 2 Shows the TEM comparison diagrams of the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. Among them, Figure 2 (a) is the TEM diagram of the spinel prepared in Comparative Example 1, Figure 2 (b) is the TEM diagram of the spinel prepared in Comparative Example 2, Figure 2 (c) is the TEM diagram of the spinel prepared in Comparative Example 3, Figure 2 (d) is the TEM diagram of the spinel prepared in Example 1, Figure 2 (e) is the TEM diagram of the spinel prepared in Comparative Example 4.

[0018] Figure 3 Shows the H 2 -TPR comparison diagrams of the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4.

[0019] Figure 4 Shows the NH 3 -TPD comparison diagrams of the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4.

[0020] Figure 5 Shows the comparison diagrams of the thermogravimetric curves of the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 after catalysis. DETAILED DESCRIPTION OF THE INVENTION

[0021] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals denote like or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0022] Example 1 Copper nitrate, aluminum nitrate, manganese nitrate and ethylene glycol with a molar ratio of 0.8:1.8:0.1:4 were dissolved in ultrapure water to obtain a precursor solution. Then, the precursor solution was placed in a water bath and heated at 60 °C for 0.5 h. After the water evaporated, a wet gel was obtained. The wet gel was calcined in air at 350 °C for 1 h. The wet gel foamed and burned to obtain a precursor powder. Finally, silica sol and the precursor powder with a mass ratio of 0.05:1 were mixed and ground, and then calcined in air at 700 °C for 3 h to obtain Mn-doped CuAl 2 O 4 spinel.

[0023] Example 2 Copper nitrate, aluminum nitrate, manganese nitrate and ethylene glycol with a molar ratio of 1.2:2.1:0.3:6 were dissolved in ultrapure water to obtain a precursor solution. Then, the precursor solution was placed in a water bath and heated at 90 °C for 1 h. After the water evaporated, a wet gel was obtained. The wet gel was calcined in air at 400 °C for 2 h. The wet gel foamed and burned to obtain a precursor powder. Finally, silica sol and the precursor powder with a mass ratio of 0.1:1 were mixed and ground, and then calcined in air at 800 °C for 4 h to obtain Mn-doped CuAl 2 O 4 spinel.

[0024] Example 3 Copper sulfate, aluminum sulfate, manganese sulfate and glycine with a molar ratio of 1.6:2.4:0.4:8 were dissolved in ultrapure water to obtain a precursor solution. Then, the precursor solution was placed in a water bath and heated at 120 °C for 2 h. After the water evaporated, a wet gel was obtained. The wet gel was calcined in air at 450 °C for 3 h. The wet gel foamed and burned to obtain a precursor powder. Finally, aluminum sol and the precursor powder with a mass ratio of 0.1:1 were mixed and ground, and then calcined in air at 900 °C for 6 h to obtain Mn-doped CuAl 2 O 4 spinel.

[0025] Example 4 Dissolve copper chloride, aluminum chloride, manganese chloride, and urea with a molar ratio of 0.8:1.8:0.1:4 in ultrapure water to obtain a precursor solution. Then, place the precursor solution in a water bath and heat it at 60 °C for 0.5 h. After the water evaporates, a wet gel is obtained. Calcinate the wet gel in air at 350 °C for 1 h. The wet gel undergoes foaming and combustion to obtain a precursor powder. Finally, mix and grind zirconia sol and the precursor powder with a mass ratio of 0.15:1, and calcinate it in air at 700 °C for 3 h to obtain Mn-doped CuAl 2 O 4 spinel.

[0026] Comparative Example 1 Dissolve copper nitrate, aluminum nitrate, manganese nitrate, and ethylene glycol with a molar ratio of 1.8:1.4:0.5:2 in ultrapure water to obtain a precursor solution. Then, place the precursor solution in a water bath and heat it at 60 °C for 0.5 h. After the water evaporates, a wet gel is obtained. Calcinate the wet gel in air at 350 °C for 1 h. The wet gel undergoes foaming and combustion to obtain a precursor powder. Finally, grind the precursor powder and calcinate it in air at 700 °C for 3 h to obtain Mn-doped CuAl 2 O 4 spinel.

[0027] Comparative Example 2 Dissolve copper nitrate, aluminum nitrate, manganese nitrate, and ethylene glycol with a molar ratio of 0.8:1.8:0.1:4 in ultrapure water to obtain a precursor solution. Then, place the precursor solution in a water bath and heat it at 140 °C for 3 h. After the water evaporates, a wet gel is obtained. Calcinate the wet gel in air at 550 °C for 0.5 h. The wet gel undergoes foaming and combustion to obtain a precursor powder. Finally, grind the precursor powder and calcinate it in air at 1000 °C for 1 h to obtain Mn-doped CuAl 2 O 4 spinel.

[0028] Comparative Example 3 Dissolve copper nitrate, aluminum nitrate, magnesium nitrate, and ethylene glycol with a molar ratio of 0.8:1.8:0.1:4 in ultrapure water to obtain a precursor solution. Then, place the precursor solution in a water bath and heat it at 60 °C for 0.5 h. After the water evaporates, a wet gel is obtained. Calcinate the wet gel in air at 350 °C for 1 h. The wet gel undergoes foaming and combustion to obtain a precursor powder. Finally, grind the precursor powder and calcinate it in air at 700 °C for 3 h to obtain Mg-doped CuAl 2 O 4 spinel.

[0029] Comparative Example 4 Copper nitrate, aluminum nitrate and ethylene glycol with a molar ratio of 0.8:1.8:4 were dissolved in ultrapure water to obtain a precursor solution. Then, the precursor solution was placed in a water bath and heated at 60 °C for 0.5 h. After the water evaporated, a wet gel was obtained. The wet gel was calcined in air at 350 °C for 1 h. The wet gel foamed and burned to obtain a precursor powder. Finally, the precursor powder was ground and calcined in air at 700 °C for 3 h to obtain pure CuAl 2 O 4 spinel.

[0030] The performance test method for the spinel-catalyzed alcohol reforming for hydrogen production is as follows: The spinel was uniformly mixed with quartz particles and filled in the middle of a tubular reactor. The two ends of the reactor were sealed with threads. Then, the tubular reactor was placed in a tubular furnace controlled by a thermocouple. After the furnace temperature rose to the set temperature, a mixed solution of alcohol and water with a molar ratio of 1:1.2 was injected into the tubular reactor using an electronic injection pump. The mixed gas of alcohol and water evaporated at the front end of the tubular reactor contacted the spinel and reacted to generate a hydrogen-rich gas. The unreacted alcohol and water were collected by a condenser. The flow rate of the reformed gas was measured using a soap bubble flowmeter, and the composition of the reformed gas was detected using a gas chromatograph. Alcohol conversion rate X Alcohol and hydrogen production V H2 were calculated according to the following formula:

[0031] where V out is the molar flow rate of the reformed gas, φ CO , φ CO 2 , φ H 2 represent the contents of carbon monoxide, carbon dioxide and hydrogen in the reformed gas, respectively, V Alcohol,in is the molar flow rate of the alcohol injected into the microreactor.

[0032] The inventors performed XRD tests on the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, and the results are as Figure 1 shown. It can be found from Figure 1 that the diffraction peaks of the spinel prepared in Example 1 are the broadest, indicating that its crystal grains are the smallest.

[0033] The inventors performed TEM tests on the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, and the results are as Figure 2 shown. FromFigure 2 It can be found that the average particle size of the spinel prepared in Example 1 is the smallest, which is 71.31 nm.

[0034] The inventors carried out H 2 -TPR tests on the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, and the results are as Figure 3 shown. From Figure 3 it can be found that the H 2 -TPR curve of the spinel shows three hydrogen consumption peaks, namely, the reduction peak of highly dispersed non-spinel phase CuO (200 - 400 °C), the reduction peak of easily reducible spinel phase CuO (400 - 600 °C), and the reduction peak of difficult-to-reduce spinel phase CuO (above 600 °C). It can be found that the amount of difficult-to-reduce spinel phase CuO in the spinel prepared in Example 1 increases.

[0035] The inventors carried out NH 3 -TPD tests on the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, and the results are as Figure 4 shown. From Figure 4 it can be found that the NH 3 -TPD curve of the spinel shows three NH 3 desorption peaks, namely, the α peak belonging to weak acid sites around 150 °C, the β peak belonging to medium acid sites around 450 °C, and the γ peak belonging to strong acid sites around 650 °C. It can be found that the acidity of the spinel prepared in Example 1 is the lowest.

[0036] The inventors carried out specific surface area and average pore diameter tests on the spinels prepared in Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, and the results are shown in Table 1. It can be found from Table 1 that the specific surface area and average pore diameter of the spinel prepared in Example 1 are the largest.

[0037] Table 1 Specific surface area and average pore diameter of spinel

[0038] The inventors applied the spinels prepared in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 to methanol reforming for hydrogen production, and characterized the methanol conversion rate, hydrogen yield, carbon monoxide selectivity and catalytic stability of the spinels at a methanol feed rate of 0.16 mol / h and 300 °C. The results are shown in Table 2. As can be seen from Table 2, compared with the spinels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, the spinels prepared in Example 1, Example 2, Example 3 and Example 4 have lower CO selectivity and more excellent catalytic activity and stability. This is because doping with foreign cations can form composite spinels, modify the surface of copper species and change the chemical environment of copper species. SiO 2 and Al 2 O 3 and ZrO 2 formed during the preparation process of the inorganic sol can block the aggregation of homogeneous particles, and the synergistic effect of the two improves the catalytic activity and stability of the spinel.

[0039] Table 2 Performance of Spinel Catalyzed Methanol Reforming for Hydrogen Production

[0040] The inventors conducted thermogravimetric tests on the spinels after catalyzing methanol reforming for hydrogen production, and the results are as Figure 5 shown. It can be found from Figure 5 that the amount of carbon deposition of the spinel prepared in Example 1 is the smallest, which is consistent with the stability results.

[0041] The inventors applied the spinels prepared in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 to ethanol reforming for hydrogen production, and characterized the ethanol conversion rate, hydrogen yield, carbon monoxide selectivity and catalytic stability of the spinels at an ethanol feed rate of 0.16 mol / h and 500 °C. The results are shown in Table 3. As can be seen from Table 3, compared with the spinels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, the spinels prepared in Example 1, Example 2, Example 3 and Example 4 have lower CO selectivity and more excellent catalytic activity and stability.

[0042] Table 3 Performance of Spinel Catalyzed Ethanol Reforming for Hydrogen Production

[0043] The inventors applied the spinels prepared in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 to the reforming of glycerol to produce hydrogen, and characterized the glycerol conversion rate, hydrogen yield, carbon monoxide selectivity and catalytic stability of the spinels at a glycerol feed rate of 0.16 mol / h and 600 °C. The results are shown in Table 3. As can be seen from Table 3, compared with the spinels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, the spinels prepared in Example 1, Example 2, Example 3 and Example 4 have lower CO selectivity and more excellent catalytic activity and stability.

[0044] Table 3 Performance of spinel in catalytic reforming of glycerol to produce hydrogen

[0045] The inventors applied the spinels prepared in Example 1, Example 2, Example 3, Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4 to the reforming of n-butanol to produce hydrogen, and characterized the n-butanol conversion rate, hydrogen yield, carbon monoxide selectivity and catalytic stability of the spinels at an n-butanol feed rate of 0.16 mol / h and 700 °C. The results are shown in Table 4. As can be seen from Table 4, compared with the spinels prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4, the spinels prepared in Example 1, Example 2, Example 3 and Example 4 have lower CO selectivity and more excellent catalytic activity and stability.

[0046] Table 3 Performance of spinel in catalytic reforming of n-butanol to produce hydrogen

[0047] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing Mn-doped CuAl2O4 spinel, characterized in that: The steps include: After dissolving copper salt, aluminum salt and manganese salt in ultrapure water, a reducing agent is added to obtain a precursor solution; placing the precursor solution in a water bath and heating it to obtain a wet gel; calcining the wet gel in air to obtain a precursor powder; The inorganic sol and the precursor powder are mixed and ground, and then calcined in air to obtain Mn-doped CuAl2O4 spinel.

2. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The copper salt includes at least one of copper nitrate, copper chloride or copper sulfate; The aluminum salt includes at least one of aluminum nitrate, aluminum chloride or aluminum sulfate; The manganese salt includes at least one of manganese nitrate, manganese chloride or manganese sulfate.

3. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The molar ratio of the copper salt, aluminum salt, manganese salt and reducing agent is 0.8-1.6:1.8-2.4:0.1-0.4:4-8.

4. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The reducing agent includes at least one of ethylene glycol, glycine, citric acid, urea, ammonium acetate, carbohydrazide and hydrazine.

5. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The mass ratio of the inorganic sol to the precursor powder is 0.05-0.15:1; The inorganic sol includes at least one of silica sol, aluminum sol or zirconium sol.

6. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The heating temperature is 60-120°C and the heating time is 0.5-2h.

7. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The calcination temperature is 350-450°C and the calcination time is 1-3h.

8. The method for preparing Mn-doped CuAl2O4 spinel according to claim 1, characterized in that: The calcination temperature is 700-900°C and the calcination time is 3-6h.

9. Use of the Mn-doped CuAl2O4 spinel prepared by the method according to any one of claims 1 to 8 in catalyzing alcohol reforming to produce hydrogen.

10. The use according to claim 9, characterized in that: The alcohols include one or more of methanol, ethanol, glycerol or n-butanol.

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