Catalyst for coal combustion and preparation method thereof

Abstract

The invention discloses a catalyst for coal combustion and a preparation method of the catalyst, and belongs to the technical field of fire coal catalysts. A carrier of the multi-metal supported catalyst is aluminum oxide / silicon dioxide nano aerogel; wherein the multi-metal supported catalyst comprises 3-5 wt% of alkali metal and oxides thereof, 10-15 wt% of transition metal and oxides thereof, 10-20 wt% of aluminum oxide and 60-75 wt% of a silicon dioxide skeleton. By compounding alkali metal and transition metal, the ignition point of coal can be reduced, and the combustion efficiency of coal is remarkably improved; the aluminum oxide / silicon dioxide nano aerogel is used as the carrier, so that the coal combustion environment can be better adapted, active components are protected from corroding a boiler, the coking phenomenon existing in coal combustion is improved, and the catalytic activity of the catalyst is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal combustion catalysts, and in particular relates to a catalyst for coal combustion and a preparation method thereof. Background Art

[0002] my country is the world's largest coal producer and consumer, with coal accounting for over 70% of its total energy output. This coal-based energy structure is unlikely to change for a long time. However, there are two major problems with coal combustion: incomplete combustion, high coal consumption, low thermal efficiency, and a significant waste of coal resources. Furthermore, coal combustion produces large amounts of smoke and harmful gases, polluting the environment.

[0003] Energy conservation and consumption reduction are enduring challenges in our daily lives and production. To improve coal resource utilization, traditional methods primarily rely on improvements to equipment and operating procedures. However, this approach requires significant investment and is complex, failing to fundamentally address issues such as large slag volumes, high combustible content, and significant waste of coal resources. To address this issue, coal-fired catalysts have been gradually introduced into production to improve coal combustion efficiency. However, a new challenge is that traditional coal-fired catalysts often contain sodium salts, potassium salts, and sulfate compounds. Long-term use can corrode the boiler and its components, and can easily form coke, impacting coal combustion efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a catalyst for coal combustion and a preparation method thereof, so as to solve the problem that traditional coal-fired catalysts corrode boilers and form coke that seriously affects combustion efficiency.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] In the first aspect, the present invention provides a catalyst for coal combustion, which is a multi-metal supported catalyst; the carrier of the multi-metal supported catalyst is alumina / silica nanoaerogel; the composition of the multi-metal supported catalyst includes 3-5wt% of alkali metals and their oxides, 10-15wt% of transition metals and their oxides, 10-20wt% of alumina and 60-75wt% of silica skeleton.

[0007] Preferably, the alkali metals and their oxides include one or more combinations of lithium, sodium, potassium and their oxides; the transition metals and their oxides include one or more combinations of titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, lanthanum and their oxides.

[0008] Preferably, the amount of the multi-metal supported catalyst used is 0.2-1% of the mass of the coal.

[0009] By adopting the above technical solution, the present invention uses a multi-metal supported catalyst to improve the coal combustion efficiency. On the one hand, the use of alkali metals and transition metals for compounding can significantly improve the coal combustion efficiency and reduce the release of harmful gases. Specifically, the transition metals and their oxides can be reduced to metals under heating conditions, and then adsorb oxygen and oxidize again to metal oxides, so that they are always in a redox state, which can accelerate the transfer of oxygen atoms from metals to carbon atoms, accelerate the diffusion rate of oxygen, and thus accelerate the coal combustion efficiency. The compounding of alkali metals can reduce the release temperature of volatiles in coal combustion and accelerate the escape velocity of volatiles, which helps to improve the combustion efficiency. In addition, the alkali metals can also enhance the chemical reaction activity of the transition metals and oxygen, accelerate the reaction of oxygen and coal, reduce solid residues and inhibit the generation of harmful gases.

[0010] On the other hand, the catalyst of the present invention is a supported catalyst. By loading multiple metals and their oxides on a carrier, it can retain a high unit catalytic activity and greatly reduce the direct contact between the metal and the boiler and ash, thereby avoiding corrosion of the boiler by metal ions. It can also improve the coking phenomenon and further improve the coal combustion efficiency.

[0011] The carrier used in the present invention is alumina / silica nano-aerogel. Compared with other carbon-based carriers, nano-aerogel has higher heat resistance and thermal insulation, can adapt to the coal combustion environment and will not cause high temperature to damage or decompose the metal and its oxides loaded inside. It also has a unique three-dimensional nanostructure and a controllable pore structure. The pore structure is also conducive to the loading of multiple metals. As a catalyst carrier, it can exhibit good catalytic activity. The pore structure is also conducive to the circulation and transfer of oxygen, increasing the contact area between oxygen and metals and their oxides, increasing the catalytic reaction rate, and further improving the burnout rate of coal combustion. At the same time, alumina is added to the nano-aerogel carrier for compounding, which can further improve the thermal stability of the catalyst, enhance the pore stability of the catalyst carrier, prevent structural collapse during coal combustion, and ensure that the catalyst can continue to play a catalytic role.

[0012] Preferably, the surface of the multi-metal supported catalyst is further modified with polyoxyethylene ether segments.

[0013] By adopting the above technical solution, alumina / silica nanoaerogel is used as a carrier, and its surface contains a large number of polar groups. When mixed with coal, these polar groups tend to attract each other, causing agglomeration, resulting in uneven distribution of the catalyst, and thus affecting the combustion efficiency of the coal. For this reason, the catalyst surface is modified with polyoxyethylene ether chain segments, which can give the catalyst hydrophobic properties, reduce agglomeration and reduce the water absorption rate of the catalyst, thereby improving the catalytic efficiency.

[0014] In addition, the introduction of polyoxyethylene ether chain segments can also form sufficient distance and repulsion between coal and catalyst, which can accelerate air circulation and replacement, catalyze the thermal decomposition reaction of coal, increase the reaction rate in the initial combustion stage, maintain the fluidity of particles, and prevent coal from coking during combustion, thereby reducing combustion efficiency.

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

[0016] S1. Under a nitrogen atmosphere, an alkali metal salt and ethyl orthosilicate are separately added to a solvent to obtain an alkali metal solution and a pre-reaction solution; the alkali metal solution is then heated to 90-100°C and stirred for 10-20 minutes, followed by the addition of the pre-reaction solution and an acidic catalyst, and the mixture is stirred for 4-5 hours to obtain an alkali metal-ethyl silicate compound;

[0017] S2. The obtained alkali metal - ethyl silicate compound and aluminum salt are added to a solvent, and a sol-gel reaction is carried out in a water bath at 50 to 60 ° C. The reaction is kept warm for 10 to 15 hours, and finally dried and ground to obtain an alkali metal - alumina / silica aerogel;

[0018] S3. Add the alkali metal-alumina / silica aerogel and transition metal salt to water, stir and disperse them, and then stir and react at 80-90°C for 6-8 hours. Finally, grind, calcine, wash, and dry to obtain a multi-metal supported catalyst, i.e., a catalyst for coal combustion.

[0019] Preferably, the aluminum salt includes a combination of one or more of aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum sec-butoxide and aluminum isopropoxide.

[0020] Preferably, the calcination temperature in step S3 is 400-450° C., and the calcination time is 4-5 hours.

[0021] Preferably, the alkali metal salt in step S1 includes a combination of one or more of a soluble lithium salt, a soluble sodium salt and a soluble potassium salt.

[0022] More preferably, the soluble lithium salt includes a combination of one or more of lithium carbonate, lithium nitrate and lithium sulfate; the soluble sodium salt includes a combination of one or more of sodium nitrate, sodium carbonate, sodium bicarbonate, sodium acetate and sodium sulfate; and the soluble potassium salt includes a combination of one or more of potassium nitrate, potassium carbonate, potassium sulfate and potassium sulfite.

[0023] Preferably, the solvent in step S1 includes a combination of one or more of ethylene glycol, n-propanol, isopropanol and n-butanol.

[0024] Preferably, the acid catalyst comprises a combination of one or more of hydrochloric acid, sulfuric acid and nitric acid.

[0025] Preferably, the solvent in step S2 is anhydrous ethanol.

[0026] Preferably, the transition metal salt in step S3 includes one or more combinations of ferric nitrate, ferric sulfate, ferric acetate, ferric chloride, copper sulfate, copper nitrate, copper chloride, nickel sulfate, nickel nitrate, cobalt nitrate, manganese sulfate, manganese chloride, manganese nitrate, titanium chloride, zinc nitrate, zinc sulfate, vanadium sulfate, and vanadium nitrate.

[0027] By adopting the above technical solution, the alkali metal and the silica precursor are first reacted to compound the alkali metal ions into the silica precursor, and then a melt-gel reaction occurs between the alkali metal and the aluminum salt, i.e., the aluminum precursor, to dope the alkali metal into the skeleton structure of the alumina / silica aerogel. The uniform distribution of the alkali metal facilitates further catalytic enhancement of the reaction activity between the transition metal and oxygen, and also prevents the escape of the alkali metal ions during use and corrosion of the boiler. The transition metal ions are then loaded onto the alumina / silica aerogel carrier by an impregnation method, and the transition metal and alkali metal are partially or completely converted into metal oxides by calcination, thereby fixing the metal ions and playing a catalytic role in promoting coal combustion.

[0028] Preferably, the multi-metal supported catalyst is further post-treated with polyoxyethylene ether segments; the post-treatment steps are: stirring and mixing the polyoxyethylene ether surfactant and the aminosilane coupling agent at 40-45° C. for 20-30 minutes, then adding the mixture to the solvent, adjusting the pH value of the solution to 4-5, stirring and reacting at 60-70° C. for 4-6 hours, then adding the multi-metal supported catalyst, raising the temperature to 70-80° C., continuing the stirring and reaction for 5-7 hours, and finally filtering and drying the mixture.

[0029] Preferably, the polyoxyethylene ether surfactant is fatty alcohol polyoxyethylene ether, with n=10-15.

[0030] Preferably, the mass ratio of the polyoxyethylene ether surfactant to the multi-metal supported catalyst is (0.1-0.2):1.

[0031] Preferably, the aminosilane coupling agent includes a combination of one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β (aminoethyl)-γ-aminopropyltrimethoxysilane, N-β (aminoethyl)-γ-aminopropylmethyldimethoxysilane, and N-β (aminoethyl)-γ-aminopropyltriethoxysilane.

[0032] Preferably, the mass ratio of the aminosilane coupling agent to the polyoxyethylene ether surfactant is (1-1.2):1.

[0033] Preferably, the solvent is an aqueous solution of ethanol or methanol.

[0034] By adopting the above technical solution, the catalyst is hydrophobized to improve its dispersibility in coal. Specifically, the present invention uses polyoxyethylene ether segments to modify the catalyst, thereby reducing catalyst agglomeration and improving coal combustion efficiency. During the preparation process, an aminosilane coupling agent acts as a bridging agent between the polyoxyethylene ether surfactant and the multi-metal supported catalyst, connecting the polyoxyethylene ether surfactant to the catalyst surface, thereby achieving surface hydrophobization of the catalyst.

[0035] Beneficial effects of the present invention:

[0036] 1. The catalyst for coal combustion in the present invention is a multi-metal supported catalyst, using a composite of alkali metals and transition metals to lower the ignition point of coal and accelerate its combustion efficiency. Furthermore, the catalyst uses alumina / silica nanoaerogel as a carrier, which is more adaptable to the coal combustion environment than other carriers. The composite alumina further improves the thermal stability of the carrier pores, protecting the catalyst's active components from corrosion in the boiler. It also enhances the catalyst's catalytic activity and reduces coking.

[0037] 2. The surface of the catalyst of the present invention is also modified with polyoxyethylene ether chain segments, which can improve the dispersibility of the catalyst, reduce agglomeration and reduce the moisture absorption rate of the catalyst, thereby improving the catalytic efficiency; and the introduction of polyoxyethylene ether chain segments can also accelerate air flow and replacement, prevent coking, and thus increase the coal combustion rate. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0039] Example

[0040] Example 1: A catalyst for coal combustion is prepared according to the following process steps:

[0041] S1. Under a nitrogen atmosphere, potassium nitrate and tetraethyl orthosilicate were separately added to ethylene glycol to obtain an alkali metal solution and a pre-reaction solution. The alkali metal solution was then heated to 90°C and stirred for 15 minutes. The pre-reaction solution and hydrochloric acid were then added, and the mixture was stirred for 4 hours to obtain an alkali metal-tetraethyl orthosilicate compound. The amount of hydrochloric acid added was 2% by weight of the tetraethyl orthosilicate.

[0042] S2. The obtained alkali metal-ethyl silicate compound and aluminum chloride were added to anhydrous ethanol, and a sol-gel reaction was carried out in a water bath at 60°C for 12 hours. Finally, the alkali metal-alumina / silica aerogel was obtained by drying and grinding.

[0043] S3. Add alkali metal-alumina / silica aerogel and transition metal salt (the transition metal salt is a mixture of iron nitrate and manganese nitrate in a mass ratio of 2:1) to water, stir and disperse, and then stir and react at 80°C for 8 hours. Finally, grind, calcine, wash and dry to obtain a multi-metal supported catalyst, i.e., a catalyst for coal combustion, wherein the calcination temperature is 450°C and the calcination time is 4 hours.

[0044] The composition of the multi-metal supported catalyst finally obtained is 4.2 wt% of metallic potassium and its oxides, 12 wt% of metallic iron and manganese and their oxides, 15.6 wt% of aluminum oxide and 68.2 wt% of silicon dioxide skeleton.

[0045] Example 2, a catalyst for coal combustion, differs from Example 1 only in that sodium carbonate is used as the alkali metal salt, and the transition metal salt is a mixture of iron nitrate and vanadium nitrate in a mass ratio of 1:1. The resulting multi-metal supported catalyst has a composition of 3.1 wt% of metallic sodium and its oxides, 10.4 wt% of metallic iron and vanadium and their oxides, 11.5 wt% of aluminum oxide, and 75 wt% of a silica skeleton.

[0046] Example 3, a catalyst for coal combustion, differs from Example 1 only in that the alkali metal salt is a mixture of sodium carbonate and potassium nitrate in a mass ratio of 1:1, and the transition metal salt is a mixture of ferric nitrate and copper nitrate in a mass ratio of 2:1. The resulting multi-metal supported catalyst has a composition of 4.9 wt% of metallic sodium and potassium and their oxides, 14.6 wt% of metallic iron and copper and their oxides, 19.7 wt% of aluminum oxide, and 60.8 wt% of a silica skeleton.

[0047] Example 4, a catalyst for coal combustion, was prepared according to the following method:

[0048] 1.5 g of a polyoxyethylene ether surfactant (AEO-12, n=12) and 1.5 g of γ-aminopropyltriethoxysilane were stirred and mixed at 45° C. for 30 min, then added to an 85% by mass ethanol aqueous solution. The pH of the solution was adjusted to 4.5. After stirring and reacting at 65° C. for 4 h, 10 g of the multi-metal supported catalyst obtained in Example 1 was added, the temperature was raised to 80° C., and the stirring reaction was continued for 6 h. Finally, the mixture was filtered and dried.

[0049] Example 5, a catalyst for coal combustion, is different from Example 4 only in that the amount of polyoxyethylene ether surfactant added is 1 g.

[0050] Example 6, a catalyst for coal combustion, is different from Example 4 only in that the amount of polyoxyethylene ether surfactant added is 2 g.

[0051] Example 7, a catalyst for coal combustion, is different from Example 4 only in that the amount of polyoxyethylene ether surfactant added is 0.5 g.

[0052] Example 8, a catalyst for coal combustion, is different from Example 4 only in that the amount of polyoxyethylene ether surfactant added is 3 g.

[0053] Comparative Example

[0054] Comparative Example 1, a catalyst for coal combustion, differs from Example 1 only in that the composition of the resulting multi-metal supported catalyst is 2.6 wt% of metallic potassium and its oxides, 8.7 wt% of metallic iron and manganese and their oxides, 15.2 wt% of aluminum oxide, and 73.5 wt% of a silica skeleton.

[0055] Comparative Example 2, a catalyst for coal combustion, differs from Example 1 only in that the final multi-metal supported catalyst comprises 6.1 wt% of metallic potassium and its oxides, 16.3 wt% of metallic iron and manganese and their oxides, 15.4 wt% of aluminum oxide, and 62.2 wt% of a silicon dioxide skeleton.

[0056] Comparative Example 3: A catalyst for coal combustion was prepared according to the following process steps:

[0057] S1. Tetraethyl orthosilicate and aluminum chloride were added to anhydrous ethanol and subjected to a sol-gel reaction in a 60°C water bath for 12 hours. The reaction was then dried and ground to produce an alumina / silica aerogel.

[0058] S2. Add alumina / silica aerogel and a transition metal salt (the transition metal salt is a mixture of ferric nitrate and manganese nitrate in a mass ratio of 2:1) to water, stir and disperse, and react at 80°C for 8 hours. Finally, grind, calcine, wash, and dry to obtain a multi-metal supported catalyst, i.e., a catalyst for coal combustion, wherein the calcination temperature is 450°C and the calcination time is 4 hours.

[0059] The composition of the multi-metal supported catalyst finally obtained is 11.9 wt% of metallic iron and manganese and their oxides, 15.6 wt% of aluminum oxide and 72.5 wt% of silicon dioxide skeleton.

[0060] Comparative Example 4: A catalyst for coal combustion was prepared according to the following process steps:

[0061] S1. Under a nitrogen atmosphere, potassium nitrate and tetraethyl orthosilicate were separately added to ethylene glycol to obtain an alkali metal solution and a pre-reaction solution. The alkali metal solution was then heated to 90°C and stirred for 15 minutes. The pre-reaction solution and hydrochloric acid were then added, and the mixture was stirred for 4 hours to obtain an alkali metal-tetraethyl orthosilicate compound. The amount of hydrochloric acid added was 2% by weight of the tetraethyl orthosilicate.

[0062] S2. The obtained alkali metal-ethyl silicate compound and aluminum chloride are added to anhydrous ethanol, and a sol-gel reaction is carried out in a water bath at 60°C. The reaction is kept warm for 12 hours. Finally, the catalyst for coal combustion is obtained by grinding, roasting, washing and drying, wherein the roasting temperature is 450°C and the roasting time is 4 hours.

[0063] The composition of the multi-metal supported catalyst finally obtained is 4.3 wt% of metallic potassium and its oxide, 15.6 wt% of aluminum oxide and 80.1 wt% of silicon dioxide skeleton.

[0064] Comparative Example 5: A catalyst for coal combustion was prepared according to the following process steps:

[0065] S1. Under a nitrogen atmosphere, potassium nitrate and tetraethyl orthosilicate were separately added to ethylene glycol to obtain an alkali metal solution and a pre-reaction solution. The alkali metal solution was then heated to 90°C and stirred for 15 minutes. The pre-reaction solution and hydrochloric acid were then added, and the mixture was stirred for 4 hours to obtain an alkali metal-tetraethyl orthosilicate compound. The amount of hydrochloric acid added was 2% by weight of the tetraethyl orthosilicate.

[0066] S2. The obtained alkali metal-ethyl silicate compound was added to anhydrous ethanol, and a sol-gel reaction was carried out in a water bath at 60°C for 12 hours. Finally, the alkali metal-silica aerogel was obtained by drying and grinding.

[0067] S3. Add alkali metal-silica aerogel and transition metal salt (the transition metal salt is a mixture of ferric nitrate and manganese nitrate in a mass ratio of 2:1) to water, stir and disperse, and then stir and react at 80°C for 8 hours. Finally, grind, calcine, wash, and dry to obtain a multi-metal supported catalyst, i.e., a catalyst for coal combustion, wherein the calcination temperature is 450°C and the calcination time is 4 hours.

[0068] The composition of the multi-metal supported catalyst finally obtained is 4.5 wt% of metallic potassium and its oxides, 12.3 wt% of metallic iron and manganese and their oxides, and 83.2 wt% of silicon dioxide skeleton.

[0069] Comparative Example 6: A catalyst for coal combustion was prepared according to the following process steps:

[0070] SAPO-34 molecular sieve is ultrasonically dispersed in water, and an aqueous solution of potassium nitrate and an aqueous solution of a transition metal salt (the transition metal salt is a mixture of iron nitrate and manganese nitrate in a mass ratio of 2:1) are added. The temperature is raised to 60°C, and the mixture is stirred and mixed for 24 hours. After drying, grinding and calcination, a catalyst for coal combustion with a molecular sieve as a carrier is obtained, wherein the catalyst composition is 4.2wt% of metallic potassium and its oxides, 12.3wt% of metallic iron and manganese and their oxides, and 83.8wt% of a molecular sieve framework.

[0071] Performance testing

[0072] 1. Coal Burnout Rate Test: According to the relevant records in the industry standard DL / T 1106-2009 "One-Dimensional Flame Furnace Test Method for Slagging Characteristics and Burnout Rate of Pulverized Coal Combustion", the catalytic combustion efficiency of the catalysts obtained in the Examples and Comparative Examples was tested on coal, wherein the catalyst addition amount was 0.5% of the mass of the coal.

[0073] 2. Slag carbon content test: The slag obtained from the combustion in Test 1 was ashed at 815±10℃ for 2h. The carbon content of the slag sample was calculated based on the mass reduction of the sample. Specifically:

[0074]

[0075] The test results of the above tests are shown in Table 1:

[0076] Table 1 Test results

[0077]

[0078] According to Table 1, in combination with Example 1, Example 2 and Example 3, it can be seen that the burnout rate and slag carbon content of Example 2 and Example 3 are not much different from those of Example 1. Example 2 and Example 3 change the proportion of raw materials and catalyst composition within the required range, which has little effect on the performance of the final catalyst and does not change the catalytic efficiency of coal combustion.

[0079] In combination with Example 1, Example 4, and Example 5 to Example 8, it can be seen that the burnout rate of Example 4 is improved compared with that of Example 1, and the carbon content of the slag is decreased. The catalyst in Example 4 is surface-treated with polyoxyethylene ether and has a certain hydrophobicity, which can reduce the phenomenon of catalyst self-agglomeration and reduce the moisture absorption rate of the catalyst. It can also improve the air circulation and conversion between the catalyst and the coal, improve the coal combustion efficiency, and reduce the occurrence of coking. The performance of Example 5 and Example 6 is not much different from that of Example 4. Example 5 and Example 6 only change the amount of polyoxyethylene ether surfactant added within the required range, and the effect on the catalyst performance is not obvious. Example 7 and Example 8 change the amount of polyoxyethylene ether surfactant added outside the required range. The reduction in the amount of addition does not have a hydrophobic effect and enhances air circulation. Excessive addition will cause the catalyst pore structure to be blocked, and the active components of the catalyst are difficult to exchange with external oxygen, and the corresponding catalytic effect cannot be achieved, resulting in an increase in coal combustion efficiency and residual carbon.

[0080] Combining Example 1 and Comparative Examples 1 to 4, it can be seen that the burnout rates of Comparative Examples 1 to 4 decreased compared to Example 1, while the carbon content of the slag increased. In Comparative Examples 1 and 2, the ratio of alkali metals to transition metals in the catalyst was varied outside the required range. As active components of the catalyst, a decrease in the ratio of alkali metals and transition metals leads to a decrease in catalytic efficiency. In Comparative Example 3, no alkali metal was added, resulting in a small decrease in the coal ignition point and a lack of promotion of the transition metal reactivity, leading to a decrease in the final combustion efficiency. In Comparative Example 4, no transition metal was added, resulting in a lack of conversion between the transition metal and oxygen, a decrease in the reactivity between oxygen and coal, a decrease in the catalytic activity of the catalyst, and a decrease in the combustion efficiency of the coal.

[0081] Combining Example 1, Comparative Example 5, and Comparative Example 6, it can be seen that the burnout rate of Comparative Example 5 and Comparative Example 6 is reduced compared to Example 1, and the carbon content of the slag is increased. The catalyst carrier in Comparative Example 5 does not contain composite alumina, and the thermal stability of the carrier voids is reduced, which will affect the catalytic effect of the catalyst active components during the coal combustion process, reduce the oxygen flow channel, and lead to an increase in coal combustion efficiency and residual carbon. In Comparative Example 6, molecular sieve is used as a carrier. On the one hand, the thermal stability during coal combustion is not as good as the nano aerogel in the present invention. On the other hand, the binding force between metals such as alkali metals and molecular sieves is insufficient, and the possibility of coking during coal combustion is significantly increased, resulting in a significant increase in the residual carbon content of coal combustion and a decrease in coal combustion efficiency.

[0082] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0083] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A catalyst for coal combustion, characterized in that: The catalyst is a multi-metal supported catalyst; the carrier of the multi-metal supported catalyst is alumina / silicon dioxide nano-aerogel; the composition of the multi-metal supported catalyst includes 3-5wt% of alkali metals and their oxides, 10-15wt% of transition metals and their oxides, 10-20wt% of aluminum oxide and 60-75wt% of silicon dioxide skeleton.

2. The catalyst for coal combustion according to claim 1, characterized in that The alkali metals and their oxides include one or more combinations of lithium, sodium, potassium and their oxides; the transition metals and their oxides include one or more combinations of titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, vanadium and their oxides.

3. The catalyst for coal combustion according to claim 1, characterized in that The surface of the multi-metal supported catalyst is further modified with polyoxyethylene ether segments.

4. The catalyst for coal combustion according to claim 1, characterized in that The amount of the multi-metal supported catalyst used is 0.2-1% of the mass of the coal.

5. A method for preparing a catalyst for coal combustion according to any one of claims 1 to 4, characterized in that: The process steps include: S1. Under a nitrogen atmosphere, an alkali metal salt and ethyl orthosilicate are separately added to a solvent to obtain an alkali metal solution and a pre-reaction solution; the alkali metal solution is then heated to 90-100°C and stirred for 10-20 minutes, followed by the addition of the pre-reaction solution and an acidic catalyst, and the mixture is stirred for 4-5 hours to obtain an alkali metal-ethyl silicate compound; S2. The obtained alkali metal - ethyl silicate compound and aluminum salt are added to a solvent, and a sol-gel reaction is carried out in a water bath at 50 to 60 ° C. The reaction is kept warm for 10 to 15 hours, and finally dried and ground to obtain an alkali metal - alumina / silica aerogel; S3. Add the alkali metal-alumina / silica aerogel and transition metal salt to water, stir and disperse them, and then stir and react at 80-90°C for 6-8 hours. Finally, grind, calcine, wash, and dry to obtain a multi-metal supported catalyst, i.e., a catalyst for coal combustion.

6. The method for preparing a catalyst for coal combustion according to claim 5, characterized in that: The aluminum salt includes one or more of aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum sec-butoxide and aluminum isopropoxide.

7. The method for preparing a catalyst for coal combustion according to claim 5, characterized in that: The calcination temperature in step S3 is 400-450° C., and the calcination time is 4-5 hours.

8. The method for preparing a catalyst for coal combustion according to claim 5, characterized in that: The multi-metal supported catalyst is also post-treated with polyoxyethylene ether segments; the post-treatment steps are: a polyoxyethylene ether surfactant and an aminosilane coupling agent are stirred and mixed at 40-45° C. for 20-30 minutes, and then added to a solvent; the pH value of the solution is adjusted to 4-5; the multi-metal supported catalyst is added after stirring and reacting at 60-70° C. for 4-6 hours; the temperature is increased to 70-80° C.; the stirring reaction is continued for 5-7 hours; and finally the catalyst is filtered and dried.

9. The method for preparing a catalyst for coal combustion according to claim 8, characterized in that: The polyoxyethylene ether surfactant is fatty alcohol polyoxyethylene ether, with n=10-15.

10. The method for preparing a catalyst for coal combustion according to claim 8, characterized in that: The mass ratio of the polyoxyethylene ether surfactant to the multi-metal supported catalyst is (0.1-0.2):1.

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