Modified alumina carrier as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalyst carriers, and particularly relates to a modified alumina carrier and a preparation method and application thereof, the modified alumina carrier comprises a modified alumina matrix and a carbon layer coating the surface of the modified alumina matrix; the mass of the carbon layer is 10-20% of the mass of the modified aluminum oxide matrix; the modified aluminum oxide matrix is prepared from the following components in percentage by mass: 1.5 to 3 percent of tin oxide, 8 to 11 percent of alkaline earth metal oxide and the balance of gamma-Al2O3. The mechanical strength and electron conductivity of the modified alumina carrier are increased by doping tin oxide and alkaline earth metal oxide, the specific surface area of the modified alumina carrier is increased by the carbon layer coating the surface of the modified alumina matrix, and the conductive network structure formed by the carbon layer has good conductivity. The electron conductivity of the modified aluminum oxide carrier is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst carriers, and particularly relates to a modified alumina carrier, a preparation method thereof, and an application thereof. Background Art

[0002] A hydrogen fuel cell is a power generation device that directly converts the chemical energy of hydrogen and oxygen into electrical energy. Its basic principle is the reverse reaction of electrolyzing water. Hydrogen and oxygen are respectively supplied to the anode and the cathode. After hydrogen diffuses outward through the anode and reacts with the electrolyte, electrons are released and reach the cathode through an external load. In this process, hydrogen reacts with oxygen to generate water, and electrical energy is produced as a by-product. A catalyst is a key material in a hydrogen fuel cell, which accelerates the electrochemical reaction of hydrogen and oxygen, thereby improving the efficiency and performance of the battery. Usually, the catalyst of a hydrogen fuel cell conducts a catalytic reaction attached to a carrier material. The high specific surface area of the carrier material can increase the contact area between the catalyst and the reactants, and improve the catalytic efficiency. As a catalyst carrier, alumina has higher thermal stability and chemical stability compared with carbon materials. However, its electron conductivity and specific surface area are lower than those of carbon materials, resulting in a decrease in the catalytic reaction efficiency when alumina is used as the carrier material of a hydrogen fuel cell catalyst.

[0003] The prior art usually adds titanium carbide to alumina to improve the electron conductivity of alumina. However, titanium carbide will occupy the pore space of alumina, and its specific surface area is relatively low. After the two are compounded, the specific surface area of the overall material will decrease. After retrieval, the Chinese patent document with the publication number CN118929711A discloses that a modified alumina catalyst carrier is prepared by adding polyethylene glycol. Although the specific surface area of alumina is improved, the problem of poor electron conductivity when it is used as a catalyst carrier material has not been solved yet. It can be seen that at present, when alumina is used as a catalyst carrier material, it still cannot meet the requirements of high electron conductivity and large specific surface area at the same time.

[0004] Therefore, there is an urgent need for a hydrogen fuel cell catalyst carrier material that simultaneously has high stability, high specific surface area, and electron conductivity. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above problems existing in the traditional technology, and provide a modified alumina carrier, a preparation method thereof, and an application thereof.

[0006] To achieve the above technical purpose and reach the above technical effect, the present invention is realized through the following technical solutions:

[0007] The present invention provides a modified alumina carrier, which includes a modified alumina matrix and a carbon layer coated on the surface of the modified alumina matrix;

[0008] The mass of the carbon layer is 10-20% of the mass of the modified alumina matrix;

[0009] The composition of the modified alumina matrix by mass percentage includes 1.5-3% of tin oxide, 8-11% of alkaline earth metal oxide, and the balance of γ-Al2O3.

[0010] Further, in the above-mentioned modified alumina support, the pore diameter of the γ-Al2O3 is 10-20 nm, the pore volume of the γ-Al2O3 is 0.6-1.0 cm 3 / g, and the specific surface area of the γ-Al2O3 ≥ 150 m 2 / g.

[0011] Further, in the above-mentioned modified alumina support, the alkaline earth metal oxide is magnesium oxide or calcium oxide.

[0012] The present invention also provides a preparation method of a modified alumina support, including the following steps:

[0013] 1) Place γ-Al2O3 in a tin salt solution, carry out an impregnation reaction to obtain an impregnated product, and subject the impregnated product to preliminary calcination to obtain a tin-containing matrix;

[0014] 2) Place the tin-containing matrix in an alkaline earth metal salt solution and ultrasonicate to obtain an intermediate product;

[0015] 3) Subject the intermediate product to calcination treatment under a protective atmosphere to obtain a modified alumina matrix;

[0016] 4) Place the modified alumina matrix in a first carbon precursor solution for primary impregnation to obtain a primary impregnated product; place the primary impregnated product in a second carbon precursor solution for secondary impregnation to obtain a carbon-containing modified alumina matrix;

[0017] 5) Subject the carbon-containing modified alumina matrix to stepwise carbonization under a protective atmosphere to obtain the modified alumina support.

[0018] Further, in step 1), the tin salt solution is a tin nitrate solution, and the pH of the tin salt solution is 1.5-2; the ultrasonic frequency of the impregnation reaction is 35-40 kHz, the temperature is 40-45 °C, and the time is 70-90 min; the temperature of the preliminary calcination is 300-350 °C, and the time is 1-1.5 h.

[0019] Further, in step 2), the alkaline earth metal salt solution is a magnesium nitrate solution or a calcium nitrate solution; the ultrasonic frequency is 20-40 kHz, and the time is 60-90 min.

[0020] Further, in step 3), the temperature of the calcination treatment is 650-700 °C, and the time is 2-4 h.

[0021] Further, in step 4), the first carbon precursor solution is a 5-10 wt% glucose solution, and the time for the first impregnation is 30-60 min; the second carbon precursor solution is a 25-59 wt% glucose solution, the ultrasonic frequency for the second impregnation is 20-25 kHz, and the time is 1-2 h.

[0022] Further, in step 5), the process of stepwise carbonization includes:

[0023] First-stage carbonization, the temperature of the first-stage carbonization is 450-500 °C, and the time is 30-40 min;

[0024] Second-stage carbonization, the temperature of the second-stage carbonization is 700-750 °C, and the time of the second-stage carbonization is 1.5-2.5 h.

[0025] The present invention also provides an application of the modified alumina support in the preparation of a hydrogen fuel cell catalyst.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. In the present invention, tin oxide and alkaline earth metal oxides are doped inside γ-Al2O3, which improves the dispersion of the catalyst and effectively improves its electron conductivity. At the same time, a carbon layer is coated on the surface of the modified alumina matrix, which increases the specific surface area of the modified alumina support, provides more attachment points for the catalyst, and thus increases the active area of the modified alumina support. In addition, the larger specific surface area is also beneficial to the uniform dispersion of catalyst particles, preventing particle aggregation and maintaining the activity and stability of the catalyst. And the carbon layer forms a conductive network on the surface of the modified alumina matrix, further improving the electron conductivity of the modified alumina support.

[0028] 2. The preparation method of the modified alumina support of the present invention is scientifically and reasonably designed. By adopting the methods of the first impregnation and the second impregnation, the penetration of the carbon precursor solution into the interior of the modified alumina matrix is reduced, so that the carbon precursor solution successfully forms a carbon layer on the surface of the modified alumina matrix. At the same time, by adopting the stepwise carbonization method, the bonding force between the carbon layer and the modified alumina matrix is improved.

[0029] Of course, it is not necessary for any product implementing the present invention to achieve all the above advantages simultaneously. Detailed Embodiments

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all 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.

[0031] The present invention provides a modified alumina support, which includes a modified alumina matrix and a carbon layer coated on the surface of the modified alumina matrix;

[0032] The mass of the carbon layer is 10-20% of the mass of the modified alumina matrix;

[0033] The composition of the modified alumina matrix, by mass percentage, includes 1.5-3% of tin oxide, 8-11% of alkaline earth metal oxide, and the balance of γ-Al2O3.

[0034] In some embodiments of the present invention, the pore diameter of γ-Al2O3 is 10-20 nm, the pore volume of γ-Al2O3 is 0.6-1.0 cm 3 / g, and the specific surface area of γ-Al2O3 ≥ 150 m 2 / g.

[0035] In some embodiments of the present invention, γ-Al2O3 is a mesoporous material, which has a higher specific surface area compared with α-Al2O3, and can provide more active sites for the catalyst. And the number of surface hydroxyl groups of γ-Al2O3 is more, which is more likely to combine with tin oxide and alkaline earth metal oxides, improving the loading uniformity.

[0036] In some embodiments of the present invention, tin oxide is an n-type semiconductor, which has oxygen vacancies by itself. These oxygen vacancies will release free electrons, thereby increasing the carrier concentration, and further improving the electron conductivity of the modified alumina support.

[0037] In some embodiments of the present invention, the alkaline earth metal oxide has a high melting point and thermal stability. When doped into γ-Al2O3, it can strengthen the lattice structure of γ-Al2O3, making it more difficult to undergo phase change or sintering at high temperatures, thereby improving the thermal stability of the modified alumina support. At the same time, the alkaline earth metal oxide can undergo a neutralization reaction with the acidic sites on the surface of γ-Al2O3, reducing the active sites on the surface of γ-Al2O3, thereby reducing the interaction between the modified alumina support and the reactants in the hydrogen fuel cell catalytic reaction, and further improving the chemical stability.

[0038] In some embodiments of the present invention, the alkaline earth metal oxide is magnesium oxide or calcium oxide. Compared with other alkaline earth metal oxides, magnesium oxide and calcium oxide have relatively low costs, and at the same time have high thermal stability and chemical stability.

[0039] The present invention also provides a preparation method of the above-mentioned modified alumina support, including the following steps:

[0040] Including the following steps:

[0041] 1) Place γ-Al2O3 in a stannous salt solution, carry out an impregnation reaction to obtain an impregnated product, and subject the impregnated product to preliminary calcination to obtain a tin-containing matrix;

[0042] 2) Place the tin-containing matrix in an alkaline earth metal salt solution and perform ultrasonic treatment to obtain an intermediate product;

[0043] 3) Subject the intermediate product to calcination treatment under a protective atmosphere to obtain a modified alumina matrix;

[0044] 4) Place the modified alumina matrix in a first carbon precursor solution for primary impregnation to obtain a primary impregnated product; place the primary impregnated product in a second carbon precursor solution for secondary impregnation to obtain a carbon-containing modified alumina matrix;

[0045] 5) Subject the carbon-containing modified alumina matrix to stepwise carbonization under a protective atmosphere to obtain a modified alumina support.

[0046] In some embodiments of the present invention, in step 1), the stannous salt solution is a stannous nitrate solution, and the pH of the stannous salt solution is 1.5 - 2; the ultrasonic frequency of the impregnation reaction is 35 - 40 kHz, the temperature is 40 - 45 °C, and the time is 70 - 90 min; the temperature of the preliminary calcination is 300 - 350 °C, and the time is 1 - 1.5 h.

[0047] In some embodiments of the present invention, the stannous nitrate solution is a Sn(NO3)4 solution, which has high water solubility and is prone to hydrolysis. Controlling the pH at 1.5 - 2 can inhibit the hydrolysis reaction and ensure that stannous nitrate is successfully impregnated into the interior of γ-Al2O3.

[0048] In some embodiments of the present invention, performing preliminary calcination in step 1) can avoid the phenomenon of agglomeration of Sn 4+ during subsequent calcination treatment, which blocks the pores. At the same time, the tin oxide generated by preliminary calcination can combine with the surface hydroxyl groups (-OH) of γ-Al2O3 through Sn-O-Al bonds during subsequent calcination treatment, improving the interfacial stability and preventing the tin oxide from falling off during the subsequent stepwise carbonization process.

[0049] In some embodiments of the present invention, due to losses during the preparation process, the actual mass fraction of the stannous salt solution needs to exceed the mass content of tin oxide in the modified alumina matrix.

[0050] Through actual operation, it is known that in step 2), the impregnation efficiency of ultrasonic treatment is 80 - 85%, and the loss rate of preliminary calcination is 2 - 6%. Therefore, when calculating based on 100% of the mass of the modified alumina matrix, in order to ensure that the prepared modified alumina matrix meets its respective composition ratio range, the mass fraction of the stannous nitrate solution is 4 - 10 wt%.

[0051] In some embodiments of the present invention, in step 2), the alkaline earth metal salt solution is a magnesium nitrate solution or a calcium nitrate solution; in step 2), the ultrasonic frequency is 20 - 40 kHz, and the ultrasonic time is 60 - 90 min.

[0052] In some embodiments of the present invention, both the magnesium nitrate solution and the calcium nitrate solution can decompose at a temperature of 300 - 400 °C to form the corresponding alkaline earth metal oxides, which matches the calcination temperature in step 3) of the present invention, ensuring that Mg exists stably in γ - Al2O3 in the form of magnesium oxide and / or Ca exists stably in the form of calcium oxide.

[0053] In some embodiments of the present invention, due to losses during the preparation process, the actual mass fraction of the alkaline earth metal salt solution needs to exceed the mass content of the alkaline earth metal oxide in the modified alumina matrix. Through actual operation, it is known that in step 2), the impregnation efficiency of ultrasonic treatment is 80 - 85%, and in step 3), the loss rate of calcination treatment is 5 - 10%. Therefore, when calculating based on 100% of the mass of the modified alumina matrix, in order to ensure that the prepared modified alumina matrix meets the range of its various composition ratios, the mass fraction of the magnesium nitrate solution is 36 - 56 wt%, and the mass fraction of the calcium nitrate solution is 28 - 45 wt%.

[0054] In some embodiments of the present invention, in step 3), the temperature of the calcination treatment is 650 - 700 °C, and the time is 2 - 4 h.

[0055] In some embodiments of the present invention, in step 3), the protective atmosphere includes nitrogen.

[0056] In some embodiments of the present invention, in step 4), the first carbon precursor solution includes a glucose solution, the concentration of the first carbon precursor solution is 5 - 10 wt%, and the time of the first impregnation is 3 - 60 min;

[0057] The second carbon precursor solution includes a glucose solution, the ultrasonic frequency of the second impregnation is 20 - 25 kHz, and the time of the second impregnation is 1 - 2 h.

[0058] In some embodiments of the present invention, through actual operation, it is known that in step 4), the impregnation efficiency of the first impregnation is 80 - 85%, and the impregnation efficiency of the second impregnation is 80 - 85%; in step 5), the carbonization efficiency of the step - by - step carbonization is 98 - 99%. Therefore, in order to ensure that the mass of the carbon layer accounts for 10 - 20% of the mass of the modified alumina matrix, the mass fraction of the second carbon precursor solution is 25 - 59 wt%.

[0059] In some embodiments of the present invention, in step 4), a first carbon precursor solution with a lower concentration is first used as the impregnating solution for primary impregnation, so that the glucose solution (carbon layer raw material) is preferentially adsorbed on the surface of the modified alumina matrix. Subsequently, during secondary impregnation, ultrasonic waves are used to promote the enrichment of the carbon layer raw material on the surface.

[0060] In some embodiments of the present invention, in step 5), the protective atmosphere includes nitrogen.

[0061] In some embodiments of the present invention, in step 5), the process of stepwise carbonization includes:

[0062] First-stage carbonization, the temperature of the first-stage carbonization is 450 - 500 °C, and the time of the first-stage carbonization is 30 - 40 min;

[0063] Second-stage carbonization, the temperature of the second-stage carbonization is 700 - 750 °C, and the time of the second-stage carbonization is 1.5 - 2.5 h.

[0064] In some embodiments of the present invention, the first-stage carbonization can promote the preferential carbonization of the carbon layer raw material on the surface of the modified alumina matrix to form a dense layer; the second-stage carbonization can carbonize the carbon layer raw material remaining inside the modified alumina matrix and promote the combination of the surface carbon layer and the modified alumina matrix.

[0065] The present invention also provides the application of the above-mentioned modified alumina carrier or the modified alumina carrier prepared by the preparation method of the above-mentioned modified alumina carrier in a hydrogen fuel cell catalyst.

[0066] The relevant specific embodiments of the present invention are as follows:

[0067] Example 1

[0068] 1) Put 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) into a tin nitrate solution with a mass fraction of 5 wt% and a pH of 2, impregnate and react at a temperature of 40 °C with an ultrasonic frequency of 35 kHz for 70 min to obtain an impregnated product, and preliminarily calcine the impregnated product at a temperature of 300 °C for 1 h to obtain a tin-containing matrix.

[0069] 2) Put the tin-containing matrix into a magnesium nitrate solution with a mass fraction of 40 wt%, and ultrasonically treat it for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0070] 3) Under a nitrogen atmosphere, calcine the intermediate product at a temperature of 650 °C for 2 h to obtain a modified alumina matrix.

[0071] 4) Place the modified alumina matrix in a 5 wt% glucose solution and impregnate it for 30 min for the first time to obtain a first impregnated product. Then place the first impregnated product in a 27 wt% glucose solution and ultrasonicate it at a frequency of 20 kHz for 1 h for the second impregnation to obtain a carbon-containing modified alumina matrix.

[0072] 5) Under a nitrogen atmosphere, keep the carbon-containing modified alumina matrix at 500 °C for 40 min for the first-stage carbonization, and then raise the temperature to 700 °C and keep it for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0073] Example 2

[0074] 1) Place 88 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.8 cm 3 / g, specific surface area 165 m 2 / g) in a stannous nitrate solution with a mass fraction of 6 wt% and a pH of 2, and impregnate and react it at a temperature of 40 °C with an ultrasonic frequency of 35 kHz for 75 min to obtain an impregnated product. Then preliminarily calcine the impregnated product at 320 °C for 1 h to obtain a tin-containing matrix.

[0075] 2) Place the tin-containing matrix in a calcium nitrate solution with a mass fraction of 35 wt% and ultrasonicate it at a frequency of 30 kHz for 80 min to obtain an intermediate product.

[0076] 3) Under a nitrogen atmosphere, calcine the intermediate product at 680 °C for 2.5 h to obtain the modified alumina matrix.

[0077] 4) Place the modified alumina matrix in a 10 wt% glucose solution and impregnate it for 50 min for the first time to obtain a first impregnated product. Then place the first impregnated product in a 30 wt% glucose solution and ultrasonicate it at a frequency of 25 kHz for 1 h for the second impregnation to obtain a carbon-containing modified alumina matrix.

[0078] 5) Under a nitrogen atmosphere, keep the carbon-containing modified alumina matrix at 450 °C for 30 min for the first-stage carbonization, and then raise the temperature to 720 °C and keep it for 2 h for the second-stage carbonization to obtain the modified alumina support.

[0079] Example 3

[0080] 1) Place 89 g of γ-Al2O3 (pore diameter 20 nm, pore volume 0.8 cm 3 / g, specific surface area 160 m 2 / g) was placed in a stannous nitrate solution with a mass fraction of 8 wt% and a pH of 1.5, and impregnated and reacted at an ultrasonic frequency of 40 kHz and a temperature of 45 °C for 80 min to obtain an impregnated product. The impregnated product was preliminarily calcined at a temperature of 350 °C for 1.5 h to obtain a tin-containing matrix.

[0081] 2) The tin-containing matrix was placed in a calcium nitrate solution with a mass fraction of 40 wt%, and ultrasonicated at a frequency of 30 kHz for 90 min to obtain an intermediate product.

[0082] 3) Under a nitrogen atmosphere, the intermediate product was calcined at a temperature of 700 °C for 2.5 h to obtain a modified alumina matrix.

[0083] 4) The modified alumina matrix was placed in a glucose solution with a mass fraction of 10 wt%, and initially impregnated for 60 min to obtain an initially impregnated product. The initially impregnated product was placed in a glucose solution with a mass fraction of 30 wt%, and ultrasonicated at a frequency of 25 kHz for 1.5 h for secondary impregnation to obtain a carbon-containing modified alumina matrix.

[0084] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina matrix was held at a temperature of 500 °C for 35 min for the first-stage carbonization, and then the temperature was raised to 750 °C and held for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0085] Example 4

[0086] 1) 87 g of γ-Al2O3 (pore diameter 15 nm, pore volume 1.0 cm 3 / g, specific surface area 160 m 2 / g) was placed in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 1.5, and impregnated and reacted at an ultrasonic frequency of 40 kHz and a temperature of 40 °C for 40 min to obtain an impregnated product. The impregnated product was preliminarily calcined at a temperature of 350 °C for 1.5 h to obtain a tin-containing matrix.

[0087] 2) The tin-containing matrix was placed in a magnesium nitrate solution with a mass fraction of 45 wt%, and ultrasonicated at a frequency of 40 kHz for 60 min to obtain an intermediate product.

[0088] 3) Under a nitrogen atmosphere, the intermediate product was calcined at a temperature of 680 °C for 4 h to obtain a modified alumina matrix.

[0089] 4) The modified alumina matrix was placed in a glucose solution with a mass fraction of 8 wt%, and initially impregnated for 30 min to obtain an initially impregnated product. The initially impregnated product was placed in a glucose solution with a mass fraction of 32 wt%, and ultrasonicated at a frequency of 20 kHz for 2 h for secondary impregnation to obtain a carbon-containing modified alumina matrix.

[0090] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina substrate was maintained at 500 °C for 40 min for the first-stage carbonization, and then the temperature was raised to 700 °C and maintained for 2.5 h for the second-stage carbonization to obtain the modified alumina support.

[0091] Comparative Example 1

[0092] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) was placed in a tin nitrate solution with a mass fraction of 5 wt% and a pH of 2, and impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. The impregnated product was preliminarily calcined at 300 °C for 1 h to obtain a tin-containing substrate.

[0093] 2) The tin-containing substrate was placed in a magnesium nitrate solution with a mass fraction of 40 wt%, and ultrasonicated at a frequency of 20 kHz for 60 min to obtain an intermediate product.

[0094] 3) Under a nitrogen atmosphere, the intermediate product was calcined at 650 °C for 2 h to obtain a modified alumina substrate.

[0095] Comparative Example 2

[0096] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) was placed in a tin nitrate solution with a mass fraction of 5 wt% and a pH of 2, and impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. The impregnated product was preliminarily calcined at 300 °C for 1 h to obtain a tin-containing substrate.

[0097] 2) Under a nitrogen atmosphere, the tin-containing substrate was calcined at 650 °C for 2 h to obtain a modified alumina substrate.

[0098] 3) The modified alumina substrate was placed in a glucose solution with a mass fraction of 5 wt%, and initially impregnated for 30 min to obtain an initially impregnated product. The initially impregnated product was placed in a glucose solution with a mass fraction of 27 wt% and ultrasonicated at a frequency of 20 kHz for 1 h for secondary impregnation to obtain a carbon-containing modified alumina substrate.

[0099] 4) Under a nitrogen atmosphere, the carbon-containing modified alumina substrate was maintained at 500 °C for 40 min for the first-stage carbonization, and then the temperature was raised to 700 °C and maintained for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0100] Comparative Example 3

[0101] 1) Place 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) in a magnesium nitrate solution with a mass fraction of 40 wt%, and ultrasonicate for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0102] 2) Under a nitrogen atmosphere, calcine the intermediate product at 650 °C for 2 h to obtain a modified alumina matrix.

[0103] 3) Place the modified alumina matrix in a glucose solution with a mass fraction of 5 wt%, impregnate for 30 min for the first time to obtain a first impregnated product, and then place the first impregnated product in a glucose solution with a mass fraction of 27 wt% and ultrasonicate for 1 h at a frequency of 20 kHz for a second impregnation to obtain a carbon-containing modified alumina matrix.

[0104] 4) Under a nitrogen atmosphere, keep the carbon-containing modified alumina matrix at 500 °C for 40 min for the first-stage carbonization, and then raise the temperature to 700 °C and keep it for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0105] Comparative Example 4

[0106] 1) Place 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2, impregnate and react at a temperature of 40 °C with an ultrasonic frequency of 35 kHz for 70 min to obtain an impregnated product, and then preliminarily calcine the impregnated product at 300 °C for 1 h to obtain a tin-containing matrix.

[0107] 2) Place the tin-containing matrix in a barium nitrate solution with a mass fraction of 40 wt%, and ultrasonicate for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0108] 3) Under a nitrogen atmosphere, calcine the intermediate product at 650 °C for 2 h to obtain a modified alumina matrix.

[0109] 4) Place the modified alumina matrix in a glucose solution with a mass fraction of 5 wt%, impregnate for 30 min for the first time to obtain a first impregnated product, and then place the first impregnated product in a glucose solution with a mass fraction of 27 wt% and ultrasonicate for 1 h at a frequency of 20 kHz for a second impregnation to obtain a carbon-containing modified alumina matrix.

[0110] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina substrate was kept at 500 °C for 40 min for the first-stage carbonization, and then the temperature was raised to 700 °C and kept for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0111] Comparative Example 5

[0112] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) was placed in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2, and impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. The impregnated product was preliminarily calcined at 300 °C for 1 h to obtain a tin-containing substrate.

[0113] 2) The tin-containing substrate was placed in a barium nitrate solution with a mass fraction of 40 wt%, and ultrasonicated for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0114] 3) Under a nitrogen atmosphere, the intermediate product was calcined at 650 °C for 2 h to obtain a modified alumina substrate.

[0115] 4) The modified alumina substrate was placed in polyacrylonitrile with a mass fraction of 5 wt%, and initially impregnated for 30 min to obtain an initially impregnated product. The initially impregnated product was placed in a glucose solution with a mass fraction of 27 wt% and ultrasonicated for 1 h at a frequency of 20 kHz for secondary impregnation to obtain a carbon-containing modified alumina substrate.

[0116] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina substrate was kept at 250 °C for 1 h for the first-stage carbonization, and then the temperature was raised to 1300 °C and kept for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0117] Comparative Example 6

[0118] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) was placed in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2, and impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. The impregnated product was preliminarily calcined at 300 °C for 1 h to obtain a tin-containing substrate.

[0119] 2) The tin-containing substrate was placed in a magnesium nitrate solution with a mass fraction of 40 wt%, and ultrasonicated for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0120] 3) Under a nitrogen atmosphere, the intermediate product is calcined at a temperature of 650 °C for 2 h to obtain a modified alumina matrix.

[0121] 4) The modified alumina matrix is placed in a glucose solution with a mass fraction of 5 wt%, and is initially impregnated for 30 min to obtain an initially impregnated product. The initially impregnated product is placed in a glucose solution with a mass fraction of 27 wt% and ultrasonicated at a frequency of 20 kHz for 1 h for secondary impregnation to obtain a carbon-containing modified alumina matrix.

[0122] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina matrix is maintained at a temperature of 750 °C for 2 h for a carbonization reaction to obtain a modified alumina support.

[0123] Comparative Example 7

[0124] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) is placed in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2, and is impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. The impregnated product is preliminarily calcined at a temperature of 300 °C for 1 h to obtain a tin-containing matrix.

[0125] 2) The tin-containing matrix is placed in a magnesium nitrate solution with a mass fraction of 40 wt% and ultrasonicated at a frequency of 20 kHz for 60 min to obtain an intermediate product.

[0126] 3) Under a nitrogen atmosphere, the intermediate product is calcined at a temperature of 650 °C for 2 h to obtain a modified alumina matrix.

[0127] 4) The modified alumina matrix is placed in a glucose solution with a mass fraction of 5 wt%, and is initially impregnated for 30 min to obtain an initially impregnated product. The initially impregnated product is placed in a glucose solution with a mass fraction of 27 wt% and ultrasonicated at a frequency of 20 kHz for 1 h for secondary impregnation to obtain a carbon-containing modified alumina matrix.

[0128] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina matrix is maintained at a temperature of 500 °C for 40 min for the first-stage carbonization, and then the temperature is raised to 850 °C and maintained for 1.5 h for the second-stage carbonization to obtain a modified alumina support.

[0129] Comparative Example 8

[0130] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) was placed in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2, and impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. The impregnated product was preliminarily calcined at a temperature of 300 °C for 1 h to obtain a tin-containing matrix.

[0131] 2) The tin-containing matrix was placed in a magnesium nitrate solution with a mass fraction of 40 wt%, and ultrasonicated for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0132] 3) Under a nitrogen atmosphere, the intermediate product was calcined at a temperature of 650 °C for 2 h to obtain a modified alumina matrix.

[0133] 4) The modified alumina matrix was placed in a glucose solution with a mass fraction of 32 wt% and impregnated for 80 min to obtain a carbon-containing modified alumina matrix.

[0134] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina matrix was kept at a temperature of 500 °C for 40 min for the first-stage carbonization, and then the temperature was raised to 700 °C and kept for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0135] Comparative Example 9

[0136] 1) 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) was placed in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2, and impregnated and reacted at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain a tin-containing matrix.

[0137] 2) The tin-containing matrix was placed in a magnesium nitrate solution with a mass fraction of 40 wt%, and ultrasonicated for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0138] 3) Under a nitrogen atmosphere, the intermediate product was calcined at a temperature of 650 °C for 2 h to obtain a modified alumina matrix;

[0139] 4) The modified alumina matrix was placed in a glucose solution with a mass fraction of 5 wt% and initially impregnated for 30 min to obtain an initially impregnated product. The initially impregnated product was placed in a glucose solution with a mass fraction of 27 wt% and ultrasonicated for 1 h at a frequency of 20 kHz for secondary impregnation to obtain a carbon-containing modified alumina matrix.

[0140] 5) Under a nitrogen atmosphere, the carbon-containing modified alumina matrix was kept at a temperature of 500 °C for 40 min for the first-stage carbonization, and then the temperature was raised to 700 °C and kept for 1.5 h for the second-stage carbonization to obtain the modified alumina support.

[0141] Comparative Example 10

[0142] 1) Place 90 g of γ-Al2O3 (pore diameter 10 nm, pore volume 0.6 cm 3 / g, specific surface area 160 m 2 / g) in a stannous nitrate solution with a mass fraction of 5 wt% and a pH of 2. Immerse and react at an ultrasonic frequency of 35 kHz and a temperature of 40 °C for 70 min to obtain an impregnated product. Calcinate the impregnated product at a temperature of 300 °C for 30 min to obtain a tin-containing matrix.

[0143] 2) Place the tin-containing matrix in a magnesium nitrate solution with a mass fraction of 40 wt%. Ultrasonic for 60 min at a frequency of 20 kHz to obtain an intermediate product.

[0144] 3) Under a nitrogen atmosphere, calcinate the intermediate product at a temperature of 650 °C for 2 h to obtain a modified alumina matrix.

[0145] 4) Place the modified alumina matrix in a glucose solution with a mass fraction of 5 wt%. Immerse for 30 min for the first time to obtain a first impregnated product. Place the first impregnated product in a glucose solution with a mass fraction of 27 wt%. Ultrasonic for 1 h at a frequency of 20 kHz for the second impregnation to obtain a carbon-containing modified alumina matrix.

[0146] 5) Under a nitrogen atmosphere, keep the carbon-containing modified alumina matrix at a temperature of 500 °C for 40 min for the first-stage carbonization, and then raise the temperature to 700 °C and keep it for 1.5 h for the second-stage carbonization to obtain a modified alumina support.

[0147] Test Example

[0148] Perform performance tests on the modified alumina supports prepared in Examples 1 to 4 and the modified alumina supports prepared in Comparative Examples 1 to 10. The results are shown in Table 1.

[0149] Among them, the specific surface area is measured by the BET specific surface area test method, the mechanical strength is tested according to the STMD6175-24 standard, and the electronic conductivity is measured by the four-probe DC resistivity test.

[0150] The test method for the specific surface area change rate is as follows: Calcinate the modified alumina supports prepared in Examples 1-4 and Comparative Examples 1-10 at a temperature of 800 °C for 2 h for heat resistance testing, and measure the specific surface area of the modified alumina support after calcination.

[0151] Specific surface area change rate (%) = (initial specific surface area - specific surface area after calcination) / initial specific surface area × 100%. The initial specific surface area is the specific surface area obtained by the BET specific surface area test method.

[0152] Table 1 Performance Test Results

[0153]

[0154] As can be seen from the data in Table 1, the specific surface area of the modified alumina support prepared by the present invention reaches 150 m 2 / g, the mechanical strength reaches 167 N / cm, the electronic conductivity reaches 7.1×10 -3 S / cm, and it has good thermal stability.

[0155] As can be seen from the data of Comparative Example 1, the carbon layer can significantly enhance the specific surface area, mechanical strength, electronic conductivity and thermal stability of the modified alumina support. As can be seen from the data of Comparative Example 2, after adding magnesium oxide to the modified alumina support, the mechanical strength can be significantly improved, the migration concentration of carriers can be changed, and then the electronic conductivity of the modified alumina support can be improved. At the same time, magnesium oxide can improve the stability of the pore structure and significantly improve the stability of the modified alumina support at high temperature. As can be seen from the data of Comparative Example 3, tin oxide can improve the mechanical strength of the modified alumina support, promote the formation of a conductive network, and then improve the electronic conductivity, and can also improve the anti-sintering strength of the modified alumina support and its thermal stability.

[0156] As can be seen from the data of Comparative Example 4, when magnesium nitrate is replaced by barium nitrate, due to the larger ionic radius of Ba 2+ ions and poor lattice stability, the generated structural pore size is thick and the specific surface area decreases; the grain boundary binding ability of BaO generated during the calcination treatment of barium nitrate is weak, and the electronic synergistic effect with tin oxide is poor, so the mechanical strength and electronic conductivity decrease; at high temperature, the grains of BaO are more likely to sinter, so the thermal stability is also relatively low. As can be seen from the data of Comparative Example 5, when the carbon precursor solution is replaced by polyacrylonitrile, due to the higher carbonization temperature of polyacrylonitrile, partial sintering of the structure of γ-Al2O3 itself occurs, resulting in a decrease in the specific surface area; and the brittleness of the polyacrylonitrile carbon layer is high, and the binding ability with γ-Al2O3 is weak, so the mechanical strength decreases; due to the change of the structure at too high temperature, the resistance of the grain boundary increases, and the specific surface area is easily lost at high temperature, resulting in a decrease in electronic conductivity and thermal stability.

[0157] It can be seen from the data of Comparative Example 6 that without adopting stepwise carbonization and directly carrying out the carbonization reaction at a relatively high temperature will cause the carbon layer to densify rapidly, with insufficient carbonization degree, blockage of pores, low bonding strength with the modified alumina matrix, resulting in a decrease in specific surface area, mechanical strength, electron conductivity and thermal stability. It can be seen from the data of Comparative Example 7 that when the second stepwise carbonization temperature is high (exceeding 700 - 750 °C), γ-Al2O3 is prone to phase transformation into α-Al2O3, resulting in the destruction of its own structure, leading to a decrease in specific surface area, mechanical strength, electron conductivity and thermal stability. It can be seen from the data of Comparative Example 8 that when the modified alumina matrix is directly impregnated into a glucose solution with a relatively high concentration without ultrasonic treatment, the glucose solution will be enriched in the pores of the modified alumina matrix, causing pore blockage, resulting in the destruction of the internal structure of the modified alumina matrix, and the formed carbon layer cannot well wrap on the surface of the modified alumina matrix, with poor continuity, reducing the bonding ability between the carbon layer and the modified alumina matrix, and further decreasing the specific surface area, mechanical strength, electron conductivity and thermal stability.

[0158] It can be seen from the data of Comparative Example 9 that if the preliminary calcination process is skipped, tin oxide will not be generated in advance. During the subsequent calcination treatment, since tin oxide does not form a stable dispersion system and cannot stably combine with α-Al2O3, the internal structure of the prepared modified alumina matrix is loose, resulting in relatively poor specific surface area, mechanical strength, electron conductivity and thermal stability compared with Example 1. It can be seen from the data of Comparative Example 10 that when the preliminary calcination time is less than 1 h, stannic nitrate is not completely converted into tin oxide, thus resulting in a decrease in specific surface area, mechanical strength, electron conductivity and thermal stability.

[0159] Application Example

[0160] Using the impregnation reduction method, 20 wt.% of metallic platinum (Pt) was loaded on the modified alumina carriers prepared in Example 1 and Comparative Examples 1 - 10, and the reduction conditions were 300 °C, H 2 / Ar (1:4) atmosphere for 2 hours to obtain the modified alumina carrier catalyst.

[0161] The cyclic voltammetry method was adopted to test the electrochemical active area of the above-mentioned modified alumina carrier catalyst, and the results are shown in Table 2.

[0162] Table 2 Test Results of Electrochemical Active Area

[0163] Case <![CDATA[Electrochemically active area (m 2 / gpt)]]> Example 1 84.2 Comparative Example 1 52.6 Comparative Example 2 63.4 Comparative Example 3 48.7 Comparative Example 4 59.8 Comparative Example 5 55.2 Comparative Example 6 70.1 Comparative Example 7 66.3 Comparative Example 8 61.5 Comparative Example 9 68.2 Comparative Example 10 58.4

[0164] It can be seen from the data in Table 2 that the incorporation of the carbon layer, alkaline earth metal oxide and tin oxide can enhance the dispersion of metallic platinum (Pt), significantly increase the electrochemical active area of the modified alumina carrier, enable better contact between metallic platinum and the reactants, and thus achieve the effect of improving the catalytic reaction rate.

[0165] From the data of Comparative Example 1, it can be seen that in the absence of a carbon layer, platinum metal cannot be effectively dispersed, resulting in a decrease in the electrochemically active area. From the data of Comparative Example 2, it can be seen that when the pore structure stability of the modified alumina support is poor, platinum metal cannot be effectively dispersed inside it, resulting in a decrease in the electrochemically active area. From the data of Comparative Example 3, it can be seen that in the absence of tin oxide (tin oxide is obtained by the decomposition of tin nitrate during calcination treatment), the decrease in specific surface area will lead to a decrease in the dispersibility of platinum metal. From the data of Comparative Example 4, it can be seen that when the alkaline earth metal oxide is replaced by barium oxide (obtained by the decomposition of barium nitrate during calcination treatment), the structure stability of the prepared modified alumina support is poor, resulting in a lower electrochemically active area.

[0166] From the data of Comparative Example 5, it can be seen that when the carbon precursor solution is replaced by polyacrylonitrile, the structure of the prepared modified alumina support has defects, resulting in catalyst enrichment and a decrease in the electrochemically active area. From the data of Comparative Example 6, when the carbon layer is over-densified, it will hinder the electron transport between platinum metal and the modified alumina support. From the data of Comparative Examples 7 and 8, it can be seen that when the pores inside the modified alumina matrix are blocked or damaged, the dispersibility of platinum metal on the modified alumina support will decrease. From the data of Comparative Examples 9 and 10, it can be seen that when tin oxide does not form a stable dispersion system, it will lead to limited dispersion of platinum metal, thereby reducing the electrochemically active area.

[0167] Long-term stability test

[0168] The modified alumina support catalysts prepared in the above Example 1 and Comparative Examples 1-10 were placed in a high-temperature and high-humidity environment for 1000 hours, and then the electrochemically active area was tested to obtain the electrochemically specific surface area of the modified alumina support after being placed in the high-temperature and high-humidity environment for 1000 hours, and the decay rate of the electrochemically specific surface area was calculated, as shown in Table 3. Among them, the high-temperature and high-humidity environment is: temperature 80 °C, relative humidity 95%.

[0169] Decay rate of electrochemically specific surface area = (Initial electrochemically specific surface area - Electrochemically specific surface area after being placed in the high-temperature and high-humidity environment for 1000 hours) / Initial electrochemically specific surface area × 100%.

[0170] The initial electrochemically specific surface area was obtained from the test in Table 2.

[0171] Table 3 Results of the decay rate of electrochemically specific surface area of Example 1 and Comparative Examples 1-10

[0172]

[0173]

[0174] As can be seen from Table 3, without the protection of the carbon layer in Comparative Example 1, metallic platinum is directly exposed to the high-temperature and high-humidity environment, resulting in a large attenuation of the electrochemical specific surface area. The modified alumina carriers prepared in Comparative Examples 2 and 3 have poor stability, resulting in a large attenuation rate of the electrochemical specific surface area in the long-term high-temperature and high-humidity environment. In Comparative Example 4, barium nitrate is used as a raw material. After barium nitrate is oxidized to barium oxide, its strong alkalinity will damage the connection between metallic platinum and the modified alumina carrier, resulting in poor stability. The carbon layers prepared in Comparative Examples 5 and 6 have poor bonding ability with the modified alumina matrix and are prone to peeling, causing metallic platinum to be directly exposed, resulting in a large attenuation of the electrochemical specific surface area. The self-structures of the modified alumina carriers prepared in Comparative Examples 7 and 8 are damaged, resulting in ineffective dispersion of metallic platinum on their surfaces, resulting in poor stability and a large attenuation rate of the electrochemical specific surface area. The self-structures of the modified alumina matrices prepared in Comparative Examples 9-10 have poor stability and are not suitable for long-term placement in a long-term high-temperature and high-pressure environment. Therefore, the attenuation rate of the electrochemical specific surface area is large.

[0175] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A modified alumina support, characterized in that, It includes a modified alumina matrix and a carbon layer coated on the surface of the modified alumina matrix; The mass of the carbon layer is 10-20% of the mass of the modified alumina matrix; The composition of the modified alumina matrix by mass percentage includes 1.5-3% of tin oxide, 8-11% of alkaline earth metal oxide, and the balance of γ-Al2O3.

2. The modified alumina support according to claim 1, characterized in that, The pore diameter of the γ-Al2O3 is 10 to 20 nm, and the pore volume of the γ-Al2O3 is 0.6 to 1.0 cm 3 / g. The specific surface area of the γ-Al2O3 is ≥150 m 2 / g.

3. A modified alumina support according to claim 1, characterized in that, The alkaline earth metal oxide is magnesium oxide or calcium oxide.

4. The preparation method of a modified alumina support according to any one of claims 1 to 3, characterized in that, It includes the following steps: 1) Place γ-Al2O3 in a tin salt solution, carry out an impregnation reaction to obtain an impregnated product, and subject the impregnated product to preliminary calcination to obtain a tin-containing matrix; 2) Place the tin-containing matrix in an alkaline earth metal salt solution and ultrasonicate to obtain an intermediate product; 3) Calcinate the intermediate product under a protective atmosphere to obtain a modified alumina matrix; 4) Place the modified alumina matrix in a first carbon precursor solution for primary impregnation to obtain a primary impregnated product; place the primary impregnated product in a second carbon precursor solution for secondary impregnation to obtain a carbon-containing modified alumina matrix; 5) Carry out stepwise carbonization on the carbon-containing modified alumina matrix under a protective atmosphere to obtain the modified alumina support.

5. The preparation method according to claim 4, wherein In step 1), the tin salt solution is a tin nitrate solution, and the pH of the tin salt solution is 1.5-2; the ultrasonic frequency of the impregnation reaction is 35-40 kHz, the temperature is 40-45 °C, and the time is 70-90 min; the temperature of the preliminary calcination is 300-350 °C, and the time is 1-1.5 h.

6. The preparation method according to claim 4, characterized in that, In step 2), the alkaline earth metal salt solution is a magnesium nitrate solution or a calcium nitrate solution; the ultrasonic frequency is 20-40 kHz, and the time is 60-90 min.

7. The preparation method according to claim 4, characterized in that, In step 3), the temperature of the calcination treatment is 650-700 °C, and the time is 2-4 h.

8. The preparation method according to claim 4, characterized in that, In step 4), the first carbon precursor solution is a 5-10 wt% glucose solution, and the time of the primary impregnation is 30-60 min; the second carbon precursor solution is a 25-59 wt% glucose solution, and the ultrasonic frequency of the secondary impregnation is 20-25 kHz, and the time is 1-2 h.

9. The preparation method according to claim 4, characterized in that, In step 5), the process of the stepwise carbonization includes: The first-stage carbonization, the temperature of the first-stage carbonization is 450-500 °C, and the time is 30-40 min; The second-stage carbonization, the temperature of the second-stage carbonization is 700-750 °C, and the time of the second-stage carbonization is 1.5-2.5 h.

10. Use of a modified alumina support according to any one of claims 1 to 3 in the preparation of a hydrogen fuel cell catalyst.

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