Environment-friendly rare earth catalyst, preparation method thereof and application of environment-friendly rare earth catalyst in promoting coal combustion

Abstract

The present application belongs to the technical field of coal combustion, and particularly relates to an environment-friendly rare earth catalyst, a preparation method thereof and application of the catalyst in promoting coal combustion. The catalyst is prepared from composite rare earth oxides, calcium oxide, potassium carbonate, ferrous sulfate, kaolin, diatomite and a specific proportion of a multi-component composite auxiliary catalyst component as raw materials through steps of slurry ultrasonic activation, rare earth coating, auxiliary catalyst stepwise doping, microwave drying and calcination in a protective atmosphere. The catalyst has a unique structure and good dispersibility, can significantly improve the coal combustion efficiency, reduce the burnout temperature and fly ash carbon content, effectively reduce the emission of flue gas pollutants such as CO, NO x and SO2, and is suitable for the fields of energy saving and carbon reduction and environmental protection treatment of coal-fired power plants and industrial boilers.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal combustion, and particularly relates to an environment-friendly rare earth catalyst, a preparation method thereof and application thereof in promoting coal combustion. BACKGROUND

[0002] Although renewable energy is developing, coal will still be an irreplaceable basic energy in the fields of power, heat, industrial production and the like in the medium and short term. However, the traditional coal combustion mode has the problems of low energy efficiency, serious pollutant emission and high carbon emission, which directly affects the environmental quality and energy utilization efficiency. Therefore, the industry widely explores the way of adding additives or catalysts to promote full combustion of coal, reduce pollutant emission and improve energy utilization efficiency.

[0003] There are various existing coal combustion improvers and coal-saving agents, including metal oxide, mineral additive, organic surfactant and composite additive. These traditional additives have certain improvement effect on the coal ignition temperature, combustion speed and part of pollutant emission in actual application, but generally have the following problems: first, the components are complex, the raw material cost is high, some additives contain heavy metals or have potential harm to the environment, and secondary pollution is easy to cause, which is contrary to the concept of green and low-carbon development; second, some components are easy to decompose or volatilize in high-temperature combustion environment, which affects the catalytic activity and service life, and the long-term application effect is unstable; third, the adaptability of some additives to different coal types is limited, and the improvement effect on low-quality coal and high-ash coal is not obvious, and the energy efficiency bottleneck caused by complex coal types in industrial boilers, kilns and the like cannot be solved. In addition, some existing products claim to save coal and reduce carbon, but in actual working conditions, due to the technical details such as adding method, catalyst particle size and uniformity of mixing with coal particles, it is often difficult to achieve the theoretical expected coal-saving rate and emission reduction effect, and even there are problems such as large amount of additive, poor economy and complicated on-site operation, which seriously restricts the popularization and application.

[0004] Especially under the background of increasing energy-saving and emission-reducing pressure, the control standards of pollutants such as carbon dioxide, nitrogen oxides and sulfur oxides in the process of coal combustion are becoming increasingly strict. In the existing technology, most of the additives have not formed a synergistic mechanism in inhibiting carbon emission, improving coal combustion efficiency and reducing harmful gas emission, and some products can only improve part of the indicators, and cannot comprehensively improve the level of clean utilization of coal in large-scale application scenarios. In addition, the preparation process of traditional additives is relatively backward, and the product quality fluctuates greatly, which is not conducive to industrialization and large-scale popularization. Therefore, the market and industry urgently need a new type of coal combustion catalyst with green components, environment-friendly, wide adaptability, simple preparation, high catalytic efficiency and good economy, so as to improve the coal combustion efficiency at the source, reduce energy consumption, reduce pollutants and carbon emission, and thus help the traditional coal industry to realize the energy-saving and carbon-reducing and high-quality development goal.

[0005] In summary, how to develop a rare earth catalyst with high efficiency, environmental protection, controllable cost, simple operation and the ability to significantly improve the efficiency of coal combustion, and the adaptability of various coal types, has become an important technical problem to be solved in the field of clean and efficient utilization of coal. SUMMARY

[0006] The purpose of the present application is to provide an environmentally friendly rare earth catalyst, its preparation method and application in promoting coal combustion, aiming to solve the problems of existing coal combustion additives in environmental safety, raw material greenization and secondary pollution that may be caused during use, to realize clean and efficient coal combustion process, and to ensure that the additives themselves are environmentally friendly and have no harmful residues, meeting the requirements of the state for clean utilization and sustainable development of coal.

[0007] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] The first aspect of the present application provides an environmentally friendly rare earth catalyst, the preparation raw materials of which include, by weight: 10-15 parts of composite rare earth oxide, 8-18 parts of calcium oxide, 4-10 parts of potassium carbonate, 3-8 parts of ferrous sulfate, 14-20 parts of kaolin, 6-12 parts of diatomite, 5-13 parts of multi-component composite catalyst component, and 60-80 parts of water.

[0009] Further, the composite rare earth oxide is composed of cerium oxide, lanthanum oxide and neodymium oxide in a mass ratio of (5-8):(1-3):(1-3).

[0010] Further, the multi-component composite catalyst component is composed of zirconium phosphate, strontium nitrate and sodium tripolyphosphate in a mass ratio of (1.2-1.4):(0.8-1.0):1.

[0011] The rare earth oxide of the present application adopts a multi-component complex design, with cerium oxide as the main component, utilizing its unique fluorite structure and Ce 3+ / Ce 4+ variable valence characteristics to dynamically release / store lattice oxygen at the combustion interface, directly catalyzing carbon oxidation reactions; lanthanum oxide acts as a structure stabilizer, neutralizing acidic intermediates generated by sulfur in the coal on its alkaline surface, reducing corrosive gas emissions, and at the same time widening the oxygen vacancy formation energy band of CeO2; the introduction of neodymium oxide is based on its unfilled 4f electron layer, which enhances electron transfer efficiency through f-d transition, forming Nd-Fe-O active clusters with Fe 2+ , accelerating free radical chain reactions. The three components are compounded in a specific ratio to construct a ternary synergistic system of "oxygen storage-sulfur fixation-electron transfer" at the atomic scale, breaking through the activity bottleneck of single rare earth catalysts.

[0012] The multi-element composite auxiliary catalytic component of the present application also adopts a multi-component complex design, zirconium phosphate is used as a proton conductor, and the layered acidic sites thereof selectively adsorb NH3 and other nitrogen-containing precursors, and through surface The acid catalysis realizes low-temperature heterogeneous denitration; SrO generated by high-temperature decomposition of strontium nitrate combines with silico-aluminates in coal ash to form a stable glass phase to wrap unburned carbon particles, and at the same time, Sr 2+ Ion replacement of Ca in the perovskite structure 2+ , and the thermal stability of the carrier is improved; sodium tripolyphosphate has the functions of dispersant and chelating agent, the chain anions thereof wrap the active metal particles to inhibit agglomeration, and through P=O bonds, the rare earth ions are coordinated to form a 'rare earth-phosphorus oxygen bridge', and the migration resistance of the active phase is enhanced.

[0013] In the basic component, calcium oxide and potassium carbonate constitute an alkali metal / alkaline earth metal catalytic system to reduce the graphitization degree of coal coke and catalyze the gasification reaction; ferrous sulfate provides Fe 2+ / Fe 3+ Redox pairs, and a d-f electron coordination channel is formed with the rare earth component to strengthen the generation of peroxide free radicals; the double-carrier architecture of kaolin and diatomite realizes gradient loading of the active component and in-situ removal of the combustion flue gas through silico-aluminate mesoporous confinement effect and biological silicon micropore adsorption. The catalyst takes rare earth as the core and realizes the synchronous leap of the coal combustion rate and environmental protection performance through multi-element synergy.

[0014] The present application provides a preparation method of the above-mentioned environment-friendly rare earth catalyst, comprising the following steps:

[0015] (1) mixing kaolin, diatomite, calcium oxide, potassium carbonate, ferrous sulfate and water, stirring to form a slurry, and performing ultrasonic treatment on the slurry;

[0016] (2) mixing the composite rare earth oxide with water to prepare a rare earth mixed solution, heating, adjusting the pH (for example, to 3.5-4.5), adding the slurry after ultrasonic treatment in step (1) into the rare earth mixed solution, stirring to react, and obtaining a rare earth-coated composite slurry;

[0017] (3) mixing the multi-element composite auxiliary catalytic component with water to prepare an auxiliary catalytic solution, dropping the auxiliary catalytic solution into the rare earth-coated composite slurry, and dropping for multiple times (for example, dropping for three times, and each time interval is 10-15 minutes), and obtaining a catalyst slurry after reaction;

[0018] (4) standing and aging the catalyst slurry, and then performing microwave irradiation drying;

[0019] (5) after the dried product is crushed and sieved, performing calcination under a protective atmosphere, introducing a reducing gas during calcination, and obtaining the environment-friendly rare earth catalyst after calcination is completed.

[0020] Further, the stirring time of step (1) is 20-40 minutes, the ultrasonic treatment frequency is 20-30 kHz, and the time is 10-20 minutes.

[0021] Further, the temperature of the temperature rising of step (2) is 60-80℃, and the stirring reaction time is 30-60 minutes.

[0022] Further, the temperature of the auxiliary catalytic solution of step (3) is controlled at 40-50℃; after adding the auxiliary catalytic solution each time, the reactants are subjected to vacuum negative pressure degassing treatment.

[0023] Further, the temperature of the standing and curing of step (4) is 80-90℃, and the time is 1-2 hours; the microwave irradiation power is 600-900W, and the time is 20-40 minutes.

[0024] Further, the temperature of the calcination of step (5) is 500-600℃, and the time is 2-4 hours; the reducing gas is H2 and Ar mixed gas, and the volume ratio of H2 is 4-10%.

[0025] The preparation process of the application realizes the directional regulation of the microstructure of the catalyst under the premise of guaranteeing environmental friendliness through multi-step precise coupling. In the slurry pre-dispersion stage of step (1), kaolin and diatomite are preliminarily infiltrated in the water phase, and then the clay particle agglomerates are dissociated and the surface silicon hydroxyl groups are activated through ultrasonic cavitation, so as to construct a high-reactivity interface for subsequent active component loading; calcium oxide and potassium carbonate preliminarily undergo partial Ca 2+ / K + ion exchange in the alkaline slurry, forming a calcium-potassium composite alkali base skeleton, and ferrous sulfate is embedded in the carrier pores in the form of Fe 2+ , laying the foundation for low-temperature catalytic activity. In the rare earth coating stage of step (2), the composite rare earth oxide is ionized in a weak acid environment, and Ce 3+ / La 3+ / Nd 3+The environmental protection type rare earth catalyst is suitable for coal-fired power plant boiler, industrial kiln and fluidized bed combustion system, and by adding 0.05% to 0.3% of the catalyst in the mass of the coal, the burnout rate can be remarkably improved, the carbon content in fly ash can be reduced, the nitrogen oxide emission can be simultaneously reduced, and the efficient conversion of coal resources and near-zero pollution emission can be realized. 2+ / Fe 3+ The redox pair is stable in the high-activity Fe 2+ state in a reducing atmosphere, and Ar gas inert environment prevents rare earth components from high-temperature sintering; finally, a three-dimensional catalytic system is formed, which takes diatomite micropore as a transport channel, kaolin sheet as a support platform, rare earth-iron oxygen cluster as an active center and zirconium phosphate network as an acid modification, and the unique 'core-shell-mesoporous' three-level structure of the system can significantly improve the oxygen diffusion rate in the coal combustion process.

[0026] The third aspect of the present application provides the application of the above-mentioned environmental protection type rare earth catalyst in promoting coal combustion.

[0027] Specifically, the environmental protection type rare earth catalyst is suitable for coal-fired power plant boiler, industrial kiln and fluidized bed combustion system, and by adding 0.05% to 0.3% of the catalyst in the mass of the coal, the burnout rate can be remarkably improved, the carbon content in fly ash can be reduced, the nitrogen oxide emission can be simultaneously reduced, and the efficient conversion of coal resources and near-zero pollution emission can be realized.

[0028] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0029] The environmental protection type rare earth catalyst of the present application realizes efficient catalysis and pollution control in the coal combustion process through the synergistic optimization of various rare earth oxides and multiple metal components. The unique preparation process design significantly improves the specific surface area and activity component dispersion of the catalyst, and the catalyst can effectively promote the complete combustion of coal, reduce the burnout temperature, improve the combustion rate and greatly reduce the unburned carbon in fly ash. Actual tests show that after adding the catalyst of the present application, the burnout rate of coal is improved, CO, NOx The harmful gas emission amount such as SO2 is obviously reduced, and the flue gas environmental protection index is obviously improved. Meanwhile, the catalyst component is safe and environmentally friendly, the raw material source is wide, the process can be industrialized and enlarged, no secondary pollution is caused in the use process, the adaptability is strong, and the catalyst component can be widely applied to different coal types and various industrial combustion systems. Compared with the prior art, the product has multiple advantages such as high efficiency, low emission and environmental friendliness, and provides solid technical support for promoting the green and low-carbon development of the coal industry. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0031] The raw materials used in the embodiments are all ordinary commercially available products unless otherwise specified, and the following sources are exemplary.

[0032] The cerium oxide was purchased from Suzhou Youzhu Nanometer Material Co., Ltd. The lanthanum oxide and neodymium oxide were purchased from Ganzhou Gaosheng New Material Co., Ltd. The calcium oxide was purchased from Lüping Yihui Calcium Industry Co., Ltd. The kaolin was purchased from Shanxi Chaopai Calcined Kaolin Co., Ltd. The diatomite was purchased from Changbai Korean Autonomous County Jinyuan Diatomite Products Co., Ltd. The zirconium phosphate was purchased from Fujian Ruisen New Material Co., Ltd. The strontium nitrate was purchased from Shandong Desheng New Material Co., Ltd. The sodium tripolyphosphate was purchased from Hebei Wanye Chemical Co., Ltd.

[0033] Embodiment 1

[0034] The present embodiment provides an environmentally friendly rare earth catalyst, and the preparation raw materials thereof comprise, by weight fraction: 13 parts of composite rare earth oxide, 12 parts of calcium oxide, 8 parts of potassium carbonate, 5 parts of ferrous sulfate, 16 parts of kaolin, 10 parts of diatomite, 9 parts of multi-component composite catalyst component, and 75 parts of water.

[0035] The composite rare earth oxide is composed of cerium oxide, lanthanum oxide and neodymium oxide in a mass ratio of 6:2:2.

[0036] The multi-component composite catalyst component is composed of zirconium phosphate, strontium nitrate and sodium tripolyphosphate in a mass ratio of 1.3:0.9:1.

[0037] The preparation method of the environmentally friendly rare earth catalyst comprises the following steps:

[0038] (1) Weigh kaolin, diatomite, calcium oxide, potassium carbonate, ferrous sulfate by proportion, add 60 parts of deionized water, put into the reaction kettle and mechanically stir at 300 rpm for 30 minutes to form a slurry, transfer the slurry to an ultrasonic reactor, treat at a frequency of 25 kHz for 15 minutes to complete the activation of the carrier and the pre-dispersion of the components.

[0039] (2) Mix the composite rare earth oxide with 10 parts of deionized water, stir to form a rare earth mixture, heat to 70°C, add 10% dilute nitric acid solution to adjust the pH to 4.0, then slowly add the slurry obtained in step (1) to the rare earth mixture, maintain a constant temperature of 70°C and stir at a speed of 400 rpm for 45 minutes to obtain a rare earth coated composite slurry.

[0040] (3) Mix the multi-component composite catalyst component with 5 parts of deionized water, heat to 45°C to prepare a catalyst solution, under continuous stirring, add the catalyst solution to the slurry obtained in step (2) in three equal portions, with an interval of 12 minutes between each addition, immediately after each addition, apply a vacuum negative pressure of -0.08 MPa to the system for 5 minutes to eliminate bubbles at the coating interface, continue to react for 20 minutes after all the drops are added to obtain a viscous catalyst slurry.

[0041] (4) Transfer the catalyst slurry to a constant temperature aging tank, stand at 85°C for 1.5 hours, after aging, the material is placed in a microwave dryer, irradiated at 750W power for 30 minutes, the final moisture content of the material is controlled at 1%.

[0042] (5) Crush the dried product through a 200 mesh sieve, load into a tube furnace, heat to 550°C at a rate of 5°C / min under argon protection, then switch to H2 / Ar mixed gas, hydrogen accounts for 6% of the total volume of the mixed gas, constant temperature calcination for 3 hours, natural cooling to room temperature, then take out, to obtain an environmentally friendly rare earth catalyst, sealed and stored.

[0043] Example 2

[0044] This example provides an environmentally friendly rare earth catalyst, which is different from example 1 in that the preparation raw materials include, by weight: composite rare earth oxide 15 parts, calcium oxide 10 parts, potassium carbonate 8 parts, ferrous sulfate 5 parts, kaolin 14 parts, diatomite 12 parts, multi-component composite catalyst component 6 parts, water 75 parts.

[0045] Comparative Example 1

[0046] This comparative example provides an environmentally friendly rare earth catalyst, which is different from example 1 in that the preparation raw materials include, by weight: composite rare earth oxide 16 parts, calcium oxide 12 parts, potassium carbonate 8 parts, ferrous sulfate 1 part, kaolin 16 parts, diatomite 10 parts, multi-component composite catalyst component 4 parts, water 75 parts.

[0047] Comparative Example 2

[0048] The present comparative example provides an environmentally friendly rare earth catalyst, which is different from Example 1 in that the composite rare earth oxide is composed of cerium oxide, lanthanum oxide, and neodymium oxide in a ratio of 2:3:6.

[0049] Comparative Example 3

[0050] The present comparative example provides an environmentally friendly rare earth catalyst, which is different from Example 1 in that the multi-component composite catalyst component is composed of zirconium phosphate, strontium nitrate, and sodium tripolyphosphate in a ratio of 0.5:1:1.

[0051] Comparative Example 4

[0052] The present comparative example provides an environmentally friendly rare earth catalyst, which is different from Example 1 in that the multi-component composite catalyst component is replaced by ethylenediaminetetraacetic acid (EDTA).

[0053] Comparative Example 5

[0054] The present comparative example provides an environmentally friendly rare earth catalyst, which is different from Example 1 in that the preparation method of the environmentally friendly rare earth catalyst comprises the following steps:

[0055] (1) Kaolin, diatomite, calcium oxide, potassium carbonate, and ferrous sulfate were weighed according to the ratio, added to 60 parts of deionized water, and placed in a reaction kettle, and 300 rpm mechanical stirring was performed for 40 minutes to obtain a slurry.

[0056] (2) The composite rare earth oxide was mixed with 10 parts of deionized water to form a rare earth mixed solution, and the slurry obtained in step (1) was slowly poured into the rare earth mixed solution, and stirring was continued at 300 rpm at room temperature for 50 minutes to obtain a rare earth coated composite slurry.

[0057] (3) The multi-component composite catalyst component was mixed with 5 parts of deionized water, stirred and dissolved at room temperature, and then added to the rare earth coated slurry obtained in step (2) at one time, and stirring was continued for 50 minutes to obtain a catalyst slurry.

[0058] (4) The catalyst slurry was poured into an oven tray and placed in a forced air drying oven, and dried at 105°C under normal pressure for 6 hours until the material was fully dried, and then cooled to room temperature.

[0059] (5) The dried product was crushed and passed through a 200 mesh sieve, and then loaded into a muffle furnace, and heated to 500°C at a rate of 10°C / min under an air atmosphere, and held at a constant temperature for 2 hours, and then naturally cooled to room temperature after the calcination was completed, and then removed to obtain an environmentally friendly rare earth catalyst.

[0060] Performance Test

[0061] The rare earth catalysts prepared in Examples 1-2 and Comparative Examples 1-5 were subjected to performance testing, and the testing method was as follows:

[0062] 1. Burnout rate improvement (%)

[0063] The catalyst was mixed with the power coal at a mass ratio of 1:500, and the mixture was loaded into a crucible and placed in a muffle furnace for combustion at 850°C for 60 minutes. After cooling, the residual ash was weighed, and the burnout rate was calculated based on the residual ash of the raw coal and the catalyst-added coal, and the improvement was compared.

[0064] 2. Carbon content in fly ash (%)

[0065] The coal and catalyst were mixed and burned according to the method in 1 above, and the fly ash after burning was collected. A certain amount of fly ash sample was weighed, and after removing all carbon by complete ignition, the remaining material was weighed, and the mass percentage of unburned carbon in the fly ash was calculated based on the mass difference before and after.

[0066] 3. Burnout temperature (°C)

[0067] The catalyst was mixed with the power coal at a mass ratio of 1:500, and the sample was placed in a thermogravimetric analyzer and heated at a rate of 10°C / min from room temperature to 700°C under air atmosphere. The weight loss curve of the sample was recorded, and when the weight loss was basically complete and tended to be stable, the corresponding temperature was the burnout temperature.

[0068] 4. Combustion rate (% / min)

[0069] The slope of the fastest weight loss stage was analyzed using the above thermogravimetric analysis data, i.e. the mass loss rate per unit time in the main combustion zone, as the combustion rate.

[0070] 5. Reduction rate of CO, NO x , SO2 emissions in flue gas (%)

[0071] The catalyst was mixed with the power coal at a mass ratio of 1:500, and the mixture was burned in a small-scale simulated combustion device, and the combustion tail gas was collected through a flue gas sampling tube. The volume concentrations of CO, NO x , SO2 were measured using a portable flue gas analyzer, and compared with the results of the blank coal combustion without catalyst, and the reduction percentages of each gas emission were calculated.

[0072] The test results are shown in Table 1.

[0073] Table 1 Performance test results

[0074]

[0075]

[0076] The performance of the catalysts in Examples 1 and 2 shows that the complex system and preparation process of the present application help the efficient, fast and clean combustion of coal, improve the catalytic performance and emission reduction effect.

[0077] In Comparative Example 1, the content of ferrous sulfate and the amount of the multi-component complex catalyst component are reduced, which weakens the iron component and the multi-component complex catalyst system in the catalyst, and affects the oxidation-reduction capacity, electron transfer capacity and multi-component synergistic catalytic capacity of the catalyst during the combustion of coal, making it difficult to effectively promote the complete combustion of coal and the emission reduction of pollutants, which reflects the necessity of the joint optimization design of iron elements and multi-component catalyst components in the present application. In Comparative Example 2, the proportion of rare earth oxides deviates from the optimal ratio, the catalytic activity decreases, the burnout temperature is high, and the burnout rate is limited, which shows that reasonable rare earth complex has a decisive role. In Comparative Example 3, the proportion of the multi-component catalyst component is not reasonable, and the zirconium phosphate is insufficient, which affects the structure and activity of the catalyst, resulting in reduced performance, and the combustion rate and emission reduction range are weaker than those of the examples. In Comparative Example 4, after EDTA replaces the inorganic catalyst system, the synergistic effect of the catalyst is basically lost, the catalytic effect is the worst, the burnout temperature is the highest, and the burnout rate and emission reduction range are the lowest, which shows that the organic chelating agent has limited effect in this system. In Comparative Example 5, the catalyst prepared by the ordinary preparation process has poor microstructure and dispersion, and low specific surface area, and the combustion performance and emission reduction range are poor, which highlights the importance of the special preparation process of the present application.

[0078] The above is the preferred embodiment of the present application, it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. An environmentally friendly rare earth catalyst, characterized in that, The raw materials for its preparation, by weight, include: 10-15 parts of composite rare earth oxide, 8-18 parts of calcium oxide, 4-10 parts of potassium carbonate, 3-8 parts of ferrous sulfate, 14-20 parts of kaolin, 6-12 parts of diatomite, 5-13 parts of multi-component composite catalyst, and 60-80 parts of water. The composite rare earth oxide is composed of cerium oxide, lanthanum oxide, and neodymium oxide in a mass ratio of (5-8):(1-3):(1-3); The multi-component composite catalyst component consists of zirconium phosphate, strontium nitrate, and sodium tripolyphosphate in a mass ratio of (1.2–1.4):(0.8–1.0):

1. The preparation method of environmentally friendly rare earth catalysts includes the following steps: (1) Mix kaolin, diatomaceous earth, calcium oxide, potassium carbonate, ferrous sulfate and water, stir to form a slurry, and then subject the slurry to ultrasonic treatment; (2) Mix the composite rare earth oxide with water to prepare a rare earth mixture, heat up, adjust the pH, add the slurry after ultrasonic treatment in step (1) into the rare earth mixture, stir and react to obtain rare earth coated composite slurry; (3) Mix the multi-component composite catalyst component with water to prepare a catalyst solution. Add the catalyst solution dropwise to the rare earth coated composite slurry in multiple batches. After the reaction, the catalyst slurry is obtained. (4) Allow the catalyst slurry to stand and mature, and then dry it by microwave irradiation; (5) After the dried product is crushed and sieved, it is roasted under a protective atmosphere. During the roasting process, a reducing gas is introduced. After the roasting is completed, an environmentally friendly rare earth catalyst is obtained.

2. A method for preparing an environmentally friendly rare earth catalyst according to claim 1, comprising the following steps: (1) Mix kaolin, diatomaceous earth, calcium oxide, potassium carbonate, ferrous sulfate and water, stir to form a slurry, and then subject the slurry to ultrasonic treatment; (2) Mix the composite rare earth oxide with water to prepare a rare earth mixture, heat up, adjust the pH, add the slurry after ultrasonic treatment in step (1) into the rare earth mixture, stir and react to obtain rare earth coated composite slurry; (3) Mix the multi-component composite catalyst component with water to prepare a catalyst solution. Add the catalyst solution dropwise to the rare earth coated composite slurry in multiple batches. After the reaction, the catalyst slurry is obtained. (4) Allow the catalyst slurry to stand and mature, and then dry it by microwave irradiation; (5) After the dried product is crushed and sieved, it is roasted under a protective atmosphere. During the roasting process, a reducing gas is introduced. After the roasting is completed, an environmentally friendly rare earth catalyst is obtained.

3. The preparation method according to claim 2, characterized in that: The stirring time in step (1) is 20 to 40 minutes, the ultrasonic treatment frequency is 20 to 30 kHz, and the time is 10 to 20 minutes.

4. The preparation method according to claim 2, characterized in that: The temperature for heating in step (2) is 60-80°C, and the stirring reaction time is 30-60 minutes.

5. The preparation method according to claim 2, characterized in that: The temperature of the catalyst solution in step (3) is controlled at 40-50℃; after each addition of the catalyst solution, the reactants are subjected to vacuum degassing.

6. The preparation method according to claim 2, characterized in that: The temperature for static curing in step (4) is 80-90°C and the time is 1-2 hours; the power of microwave irradiation is 600-900W and the time is 20-40 minutes.

7. The preparation method according to claim 2, characterized in that: The roasting temperature in step (5) is 500-600℃ and the time is 2-4 hours; the reducing gas is a mixture of H2 and Ar, with H2 accounting for 4-10% of the volume.

8. The application of the environmentally friendly rare earth catalyst according to claim 1 in promoting coal combustion.

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