High-temperature rare earth composite oxide catalytic functional coating, preparation method and application thereof

Abstract

The application discloses a high-temperature rare earth composite oxide catalytic functional coating, a preparation method and application thereof, and adopts an atmospheric plasma flame spraying method to arrange a certain thickness of a rare earth composite oxide functional coating on the surface of a burner wall, the coating can realize catalytic combustion C x H y and catalytic reduction of NO x by improving the migration and exchange rate of active oxygen species between a gas phase flame and a solid wall. The rare earth composite oxide takes a Y2O3-ZrO2 solid solution material rich in a large number of active oxygen vacancies as a core structure, takes rare earth metal oxides and alkaline earth metal oxides as a shell structure, and is directionally designed into a core-shell functional coating material Y2O3-ZrO2@M x O y with high activity, high stability and low cost. The coating material is applied in various combustion systems, and can realize the synergistic control of high combustion efficiency and low NO x emission in the near-wall flame area.

Description

Technical fields:

[0001] This invention relates to the field of combustion technology, specifically to a high-temperature rare earth composite oxide catalytic functional coating, its preparation method, and its application. Background technology:

[0002] Natural gas (mainly methane CH4), as an abundant, clean, and low-carbon energy source, serves as an energy bridge in the transition from fossil fuels to non-fossil fuels, a crucial contributor to accelerating the construction of a green and sustainable energy system, and a vital link in achieving carbon peaking and carbon neutrality. Currently, selective catalytic / non-catalytic reduction denitrification and low NOx... x Combustion technology is a widely used method for low-NOx control. The former uses reducing agents to treat flue gas, but its economic efficiency and operability still need improvement for the widespread use of small and medium-sized industrial boilers / kilns. The latter mainly involves reducing the temperature of the low main combustion zone and creating a localized reducing atmosphere, but it has always been difficult to solve the problem of balancing pollutant emission reduction and thermal efficiency improvement. However, for clean natural gas, various conventional high-efficiency low-NOx combustion technologies can be employed, including staged air combustion and low NOx combustion. x Burners, flue gas recirculation, and staged fuel combustion still generate a considerable amount of various pollutants (including NO). x It is difficult to achieve high combustion efficiency and low NO (including CO and unburned HC). x The bottleneck lies in balancing emission efficiency. This is because, fundamentally, the core strategies of these technologies involve reducing the temperature or oxygen concentration in the main combustion zone, shortening the residence time of oxygen in the high-temperature zone, or reducing NO in the exhaust gas. x Measures such as reduction have various unavoidable defects in their technology, which restricts their widespread application in actual industry.

[0003] The development and progress of combustion science requires researchers to continuously deepen their understanding of the various mechanisms and interactions present in actual combustion processes, thereby continuously iterating and developing new combustion technologies. Flame-wall interaction, as a fundamental combustion phenomenon, involves a complex system of coupled gas dynamics, thermodynamics, and chemical reaction kinetics. It is prevalent in actual combustion equipment such as internal combustion engines, gas turbines, and industrial boilers, and has a significant impact on the energy utilization efficiency and the formation and evolution of nitrogen-containing pollutants in combustion systems. Among these interactions, the chemical interaction between the flame and the wall occurs in the near-interface region. By changing the type or physicochemical properties of the surface material, the pathway and rate of surface reactions can be controlled, thereby regulating the combustion process in the gas phase space. This has gradually become one of the important means of overall combustion process control. Summary of the Invention:

[0004] This invention provides a high-temperature rare-earth composite oxide catalytic functional coating, its preparation method, and its application. Using rare-earth composite oxides as raw materials, a catalytic functional coating is prepared to regulate the path and rate of surface reactions, thereby enhancing the migration and exchange rate of active oxygen species between the gas-phase flame and the solid wall during the gas-phase combustion process, and simultaneously achieving catalytic combustion of C. x H y and catalytic reduction of NO x This reduces pollutant emissions and solves the problems of low combustion efficiency and high nitrogen oxide emissions in the near-wall flame area of ​​existing technologies.

[0005] This invention is achieved through the following technical solutions:

[0006] A high-temperature rare earth composite oxide catalytic functional coating is applied inside a burner. The coating material is a core-shell structured functional material Y2O3-ZrO2@M x O y Using Y2O3-ZrO2 solid solution material as the core structure, with M x O y The additive material has a shell structure; M x O y The additives include rare earth metal oxides and alkaline earth metal oxides.

[0007] Preferably, the Y2O3-ZrO2 solid solution material comprises 70-80% Y2O3 and 20-30% ZrO2 by mass percentage, based on a total mass percentage of 100%.

[0008] Preferably, M is calculated as 100% of the total mass. x O y The additive materials include 45-55% rare earth metal oxides and 45-55% alkaline earth metal oxides by mass.

[0009] Preferably, the rare earth metal oxide is CeO2, La2O3, Gd2O3, Tb7O4, Sc2O3, or Pr6O. 11 The alkaline earth metal oxide is BaO, which is any one or more combinations thereof.

[0010] Preferably, M is calculated as 100% of the total mass. x O y The auxiliary materials include CeO2 with a mass fraction of 20-25%, Tb7O4 with a mass fraction of 20-25%, and BaO with a mass fraction of 50-60%.

[0011] Preferably, the thickness of the high-temperature rare earth composite oxide catalytic functional coating is 300μm to 600μm.

[0012] Y₂O₃-ZrO₂ composite oxide materials combine the advantages of acid / basic centers on the fluorite-type ZrO₂ surface with abundant oxygen vacancies on the C-type cubic Y₂O₃ surface, exhibiting both enhanced combustion and direct high-temperature NO degradation. x Characteristics; at the same time, as an important component of ceramic thermal barrier coating materials, its low solid-phase thermal conductivity also greatly reduces the heat loss from the flame to the wall.

[0013] In terms of combustion enhancement, rare-earth catalytic functional coating materials with high lattice oxygen concentration can exhibit certain oxygen release catalytic capabilities during high-temperature reactions. In other words, active oxygen ions inside the material can migrate from the bulk lattice to the material surface through interlattice defects and occupy surface active sites, thereby reacting with free or adsorbed gaseous spatial components to promote surface catalysis of fuel. However, the intrinsic oxygen vacancy concentration of a single metal oxide is limited, which greatly restricts the active processes of gaseous oxygen molecules on the material surface.

[0014] In view of this, the present invention also protects the preparation method of the Y2O3-ZrO2 solid solution material, which uses flame spray pyrolysis (FSP) to prepare nanoscale composite metal oxide spherical particles Y2O3-ZrO2 with high crystallinity and purity. The specific steps are as follows: First, Zr(NO3)4·5H2O and Y(NO3)3·6H2O are dissolved in anhydrous ethanol solution to form a precursor solution of 0.5-0.7 mol / L; the precursor solution is injected into the solution by a micro-injection pump at a rate of 3-4 ml. The precursor spray is formed by injecting oxygen at a flow rate of 5-7 L / min into the external mixing two-phase nozzle. The precursor spray is then ignited by an auxiliary ignition flame gas. Finally, it undergoes processes such as pyrolysis, nucleation, surface growth, condensation and agglomeration to form a Y2O3-ZrO2 solid solution. The ignition flame gas has a flow rate of CH4 of 1.25-1.5 L / min, an O2 flow rate of 3.2-3.5 L / min and an Ar flow rate of 5.0-6.0 L / min.

[0015] The highly dispersed Y₂O₃-ZrO₂ nanoparticles with metastable structures possess abundant oxygen coverage on their surfaces, effectively counteracting the quenching effect of gas-phase free radicals on the wall surface and generating sufficient active components to promote the gas-phase combustion process. Furthermore, the particle size of Y₂O₃-ZrO₂ particles can be autonomously controlled by adjusting parameters such as the air-fuel ratio of the methane-assisted flame and the height of the particle collection disk. This self-nominated "self-oxygenating" combustion enhancement process essentially comprises three sub-processes: lattice oxygen extraction reaction, oxygen vacancy regeneration reaction, and lattice oxygen re-oxidation reaction.

[0016] 1. Lattice oxygen extraction reaction:

[0017] Because electrophilic oxygen species with low free energy and surface lattice oxygen species have higher oxidation activity, hydrocarbon fuels C in high-temperature combustion... x H y The intermediate species formed by cleavage (such as free radicals CH3, CH2O, CH, CO, H, etc.) tend to attack surface active sites, resulting in lattice oxygen extraction reactions.

[0018] CH3 * +[O 2- ]+[*]→CH2 * +OH -* +[V]+e - (1)

[0019] CH2O * +[O 2- ]+[*]→CHO * +OH -* +[V]+e - (2)

[0020] CH * +[O 2- →CHO * +[V]+e - (3)

[0021] CO * +[O 2- →CO2 * +[V]+2e - (4)

[0022] H * +[O 2- ]→OH -* +[V]+e - (5)

[0023] 2. Oxygen vacancy regeneration reaction:

[0024] The extraction reaction of lattice oxygen produces a large number of surface-adsorbed hydroxyl groups (OH-). -* The catalytic functional coating continues to diffuse on its surface, recombining to generate H2O or H2, while simultaneously releasing a large number of electrophilic active oxygen ions into the gas-phase flame zone. Active oxygen ions (O2) - It is highly reactive and readily transforms into superoxide ions or dissociates directly under high temperatures, thereby improving the flame chemical reaction kinetics and significantly enhancing overall combustion intensity and efficiency. Furthermore, the restored oxygen vacancies provide new bulk lattice oxygen for the next "self-oxygenation" cycle. The specific oxygen vacancy regeneration reaction is as follows:

[0025] 2OH -*→H2+2O -* (6)

[0026] 2OH -* →H2O+O -* +[*]+e - (7)

[0027] 3. Lattice oxygen re-oxidation reaction

[0028] As oxygen ions are continuously reduced by various species in the gas phase flame, the bulk lattice oxygen content of rare earth catalytic functional coating materials decreases rapidly. However, most catalyst materials cannot well match the release and storage rate of active oxygen ions, resulting in a deterioration in combustion enhancement effect.

[0029] Therefore, the present invention also protects Y2O3-ZrO2@M x O y An optimized preparation method for core-shell structured catalysts is as follows: a Y2O3-ZrO2 solid solution material is prepared by flame spray pyrolysis, and then M is sprayed downstream of the FSP spray flame. x O y The shell precursor solution is controlled by maintaining a concentration of 0.5-0.7 mol / L, and the total flow rate of the carrier gas Ar carrying the precursor solution is maintained at 5 L / min. The injection position is 30 cm above the burner to control the appropriate shell thickness.

[0030] Preferably, a CeO2 shell precursor solution Ce(NO3)3·6H2O (cerium nitrate) or a La2O3 shell precursor solution La(NO3)3·6H2O (lanthanum nitrate) is sprayed downstream of the FSP spray flame. The appropriate shell thickness (generally controlled between 5 and 50 nm) can be autonomously controlled by adjusting the precursor solution concentration and spraying position.

[0031] Y2O3-ZrO2@CeO2 / BaO and Y2O3-ZrO2@La2O3 / BaO are two core-shell structure functional materials. The CeO2 or La2O3 in the outer shell not only further enhances the material's heat resistance, but also, as n-type semiconductors with excellent oxygen storage and release properties, CeO2 or La2O3, when reduced, forms oxygen-deficient compounds. These compounds readily adsorb large amounts of oxygen and rapidly oxidize when exposed to an oxygen-rich atmosphere. With the assistance of the shell additives, oxygen ions are transferred, and the high-temperature dissociated gaseous oxygen molecules can quickly replenish the oxygen consumed by the lattice within the Y2O3-ZrO2 core, thus maintaining the stability of the functional coating's catalytic activity over a long period. The entire oxygen ion migration and transformation pathway can be described as: O2 → O2(ads) → O2 - (ads)→O2 -2 (ads)→2O- (ads)→2O 2- (lat)→2O - (ads)→O 2- The dynamic oxygen species transport equilibrium process of multi-component rare earth catalytic functional materials can adapt to changes in parameters such as reaction residence time, oxygen molecule concentration, and reaction temperature under different burner operating conditions, achieving combustion enhancement over a wide range. In the high-temperature environment of the combustion process, the stretching vibration and charge transport speed between atoms within the functional coating material are accelerated, thereby further promoting the migration of bulk active oxygen to the surface, making the chemical effect of coating-enhanced combustion more significant.

[0032] Regarding the reduction of nitrogen oxides, NO x NO accounts for over 95% of emissions, making NO removal and emission reduction paramount. The unique low coordination number environment of rare earth metal ions determines their excellent NO adsorption capacity. C-type cubic Y₂O₃, with its double-sided fluorite structure featuring a uniform distribution of 1 / 4 oxygen vacancies, has a larger cell volume, further facilitating NO decomposition. Introducing ZrO₂, with its excellent thermal and chemical properties, to form a Y₂O₃-ZrO₂ solid solution structure can further enhance NO decomposition activity and high-temperature stability. On the other hand, alkalinity is also a crucial factor for rare earth composite oxides suitable for NO catalytic reduction. The activity of NO catalytic reduction increases with the strength of alkaline sites on the catalyst material surface, thereby significantly improving the oxygen inhibition and water poisoning resistance of the catalytic functional coating material. Among these, BaO (barium oxide), CuO (copper oxide), Gd₂O₃ (gadolinium oxide), Tb₇O₄ (terbium oxide), Sc₂O₃ (scandium oxide), and Pr₆O₃ are suitable for NO catalytic reduction. 11 Praseodymium oxide exhibits high activity and is suitable as a Y2O3-ZrO2@M x O y Suitable materials for the catalyst shell structure.

[0033] During high-temperature combustion, the temperature in the core reaction zone often exceeds 1300℃, at which point the thermal NO content increases exponentially. Simultaneously, the combustion flue gas containing high concentrations of NO continues to diffuse along with the rare-earth catalytic functional coating Y2O3-ZrO2@BaO / CuO / Gd2O3 / Tb7O4 / Sc2O3 / Pr6O on the burner wall, driven by the spatial component concentration gradient. 11 Contact occurs, and a high-temperature catalytic reduction process of NO is carried out to control nitrogen-containing pollutants at the source during high-temperature combustion. This self-proclaimed "self-reducing" NO degradation process essentially includes three sub-processes: N2 generation and desorption reaction, O2 generation and desorption reaction, and nitrate formation side reaction.

[0034] 2NO + 2[*] → 2NO *(8)

[0035] 2NO * →N2O * +O * (9)

[0036] N2O * →N2 * +O * (10)

[0037] NO+O * →NO2 * (11)

[0038] NO2 * →O * +NO (12)

[0039] 2O * →O2+2[*] (13)

[0040] NO2 * +O * →NO3 * (14)

[0041] First, NO molecules adsorb onto the active sites ([*]) on the surface of the rare earth catalytic functional coating to form nitrosyl groups (NO). * Adsorbed species of NO * Generate N2O adsorbent species (N2O) * ) and surface-adsorbed oxygen species (O * Meanwhile, under high-temperature conditions, N2O species rapidly decompose into N2 and new surface-adsorbed oxygen species. NO* is also oxidized by surface-adsorbed oxygen to nitrite species (NO2). * The nitrogen further dissociates into NO and O2 molecules. After complete desorption, the exposed active sites are regenerated and enter the next cycle, achieving autocatalytic reduction of NO in high-temperature flue gas without the need for toxic reducing agents such as ammonia or urea. Furthermore, NO2... * Further oxidation may produce nitrates (NO3). * Species are strongly adsorbed on the surface of the functional coating, inhibiting the catalytic reduction activity of NO. However, this can be mitigated by using catalyst shell materials such as BaO, CuO, Gd2O3, Tb7O4, Sc2O3, or Pr6O. 11 Design can promote NO2 * →O * The forward reaction of NO proceeds, thereby accelerating the desorption of O2 from its surface and significantly inhibiting the formation of nitrate species as a byproduct. Therefore, direct catalytic reduction of NO at high temperatures is achieved.

[0042] This invention also provides a method for preparing the above-mentioned high-temperature rare earth composite oxide catalytic functional coating, comprising the following steps: core-shell structured functional material Y2O3-ZrO2@M x O y After drying, the mixture is ball-milled with a polyvinyl alcohol solution and pumped into a spray drying tower to prepare spherical agglomerated powder. After cleaning the substrate wall, a NiCoCrAlY adhesive layer is sprayed on. Then, after vacuum heat treatment, the powder is fed under vacuum at high temperature and sprayed using an atmospheric plasma spraying system.

[0043] Specifically, the following steps are included:

[0044] S1, using core-shell structured functional materials Y2O3-ZrO2@M x O y Place in an oven to dry at a temperature of 70℃~120℃ for 2-4 hours;

[0045] S2, the dried core-shell functional material Y2O3-ZrO2@M obtained in step S1 x O y The particles are mixed with a 1-5 wt% polyvinyl alcohol solution and mixed in a ball mill for more than 8 hours to obtain a slurry for spray granulation. The slurry is then pumped into a spray drying tower. The outlet temperature in the granulation parameters is set to 105℃~115℃ and the inlet temperature is set to 215℃~225℃ to finally obtain spherical agglomerated powder.

[0046] S3. Before thermal spraying, clean the wall substrate with acetone solution to remove oil stains, then use a corundum abrasive wheel to sandblast and roughen the surface until there is no metallic luster, then clean with alcohol and dry with electric hot air.

[0047] S4. After pretreatment, fix the treated substrate on the workbench, close the vacuum chamber and start evacuating to 0.3-0.5 mbar, then introduce argon gas. When the pressure rises to 100-120 mbar, ignite. After ignition, evacuate the chamber pressure to 80-100 mbar to preheat the substrate. The preheating temperature is set to 500℃~600℃. After the temperature stabilizes, start spraying the bonding layer NiCoCrAlY. Based on a total mass percentage of 100%, the proportion of each element in the bonding layer NiCoCrAlY is: Cr=20.0%, Co=24.0%, Y=0.76%, Ni=46.14%, Al=9.1%. The particle size requirement for Ni, Cr, and Al is 500 mesh, and the particle size requirement for Y and Co is 200 mesh.

[0048] S5. After the adhesive layer in step S4 is prepared, the sample is subjected to vacuum heat treatment, then the adhesive layer sample is polished with sandpaper, and then placed in alcohol and sonicated for several minutes to maintain the surface roughness below 2μm and the adhesive layer thickness is 50μm to 100μm.

[0049] S6. Fix the sample processed in step S5 on the stage, close the chamber door, turn on the vacuum system, add argon gas and then ignite the spray gun; adjust the chamber pressure and preheat the sample directly; when the infrared thermometer detects that the sample surface temperature has reached the set temperature, start feeding powder, feed the spherical agglomerated powder obtained in step S2 into the system, and after stabilization, use the atmospheric plasma spraying system for spraying operation.

[0050] S7. During the spraying process, oxygen is supplied to the vacuum chamber to prevent excessive oxygen loss from the crystal structure of the coating material. After spraying 2-4 times, the powder feeder is stopped and the flame is turned off. After the sample has cooled to room temperature, air is introduced to open the chamber and remove Y2O3-ZrO2@M. x O y Coating materials.

[0051] Preferably, in step S2, the solid-liquid mass ratio is (0.8-1):(1.2-1.5).

[0052] Preferably, in step S6, the vacuum system is turned on to evacuate to 0.5-0.8 mbar, argon gas is added to 40-45 mbar, the spray gun is ignited, the chamber pressure is adjusted to 1.5-2 mbar, and the sample preheating temperature is 950-1000℃.

[0053] This invention also provides the application of the above-mentioned rare earth composite oxide catalytic functional coating in micro-combustion engines, while simultaneously achieving catalytic combustion of C x H y and catalytic reduction of NO x Applications in [the field].

[0054] The rare earth composite oxide Y2O3-ZrO2@M x O y Different catalytic functional modules can be designed and arranged within the burner according to actual industrial needs, including wall coatings, integral honeycomb structures, porous media regenerators, and solid sintered sleeves. Rare earth catalytic functional coating units are designed according to the burner's geometry as integral or split structures such as rectangles, squares, and cylinders to achieve synergistic control of combustion enhancement and nitrogen oxide degradation. The thermal expansion coefficient of rare earth composite oxide materials is close to that of commonly used wall steel materials, while also possessing low thermal conductivity, oxidation resistance, and thermal erosion resistance. This effectively prevents high heat from the combustion flame from being transferred to the burner substrate, thereby increasing the operating temperature.

[0055] To improve the bonding strength of the coating material, a NiCoCrAlY adhesive layer is first sprayed onto the substrate surface, and the sample is subjected to vacuum heat treatment to accelerate the diffusion of elements between the adhesive layer and the substrate, thereby reducing internal defects and residual stress in the coating. Finally, a small amount of high-temperature binder can be added to further increase the adhesion of the rare earth catalytic functional coating and extend the service life of the coating.

[0056] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0057] 1. This invention relates to a high-temperature rare-earth composite oxide catalytic functional coating that simultaneously achieves combustion enhancement and nitrogen oxide reduction. Through the rational design of the types and proportions of rare-earth composite oxide core-shell structure materials, and based on the intrinsic laws of flame-wall interaction in the combustion system, and the active regulation of oxygen migration and conversion in the bulk lattice of the material under high-temperature conditions, a combustion field energy-mass cycle is constructed to achieve coordinated and effective matching of gas-phase combustion and surface catalysis. This breakthrough overcomes the limitations of existing low-NOx combustion technologies in achieving high combustion efficiency and low NOx reduction. x The bottleneck problem of balancing emissions can provide technical guidance for the research and development of key combustion technologies for cleaner use of natural gas.

[0058] 2. The high-temperature rare earth oxide catalytic functional coating wall surface proposed in this invention uses commonly used wall surface materials of combustion equipment as the substrate, and Y2O3-ZrO2@M x O y The core-shell structured rare earth composite oxide is a high-temperature catalytic active component. By using a suspension feeding method, it overcomes the problems of poor powder flowability and difficulty in powder feeding during spraying. The plasma spray gun is used to prepare a functional coating with a smooth and uniform surface and a columnar structure, which can significantly improve the bonding strength between the coating and the substrate. Moreover, its active component formulation and preparation process are green and pollution-free, and it has broad application prospects in the selection and design of combustion chamber wall materials for internal combustion engines, gas turbines, rocket engines, and aero engines. Attached image description:

[0059] Figure 1 This is a schematic diagram illustrating the technical principle of the rare earth catalytic functional coating of the present invention, which simultaneously achieves combustion enhancement and nitrogen oxide reduction.

[0060] Figure 2 This is a TEM image of the Y2O3-ZrO2@CeO2 / BaO rare earth composite oxide catalyst synthesized by spray pyrolysis in Example 2.

[0061] Figure 3 The variation of the methane / air premixed flame quenching distance with wall temperature under the action of different wall coating materials in Example 7.

[0062] Figure 4 The NO emission concentration in the exhaust gas of methane / air premixed flame combustion varies with the equivalence ratio under the action of different wall coating materials in Example 7.

[0063] Figure 5 The difference in critical flameout distance and NO emission concentration in combustion exhaust gas between methane / air premixed flames under the action of wall coating materials with different shell structures in Example 7 is shown.

[0064] Figure 6 The NO emission concentration in the exhaust gas of methane / air premixed flame combustion of different wall coating materials in Example 7 changes with operating time.

[0065] Figure 7 The combustion temperature change in the central streamline direction of the methane-doped ammonia flame under the action of the high-temperature rare earth catalytic functional coating material Y2O3-ZrO2@CeO2 / Tb7O4 / BaO in Example 7.

[0066] Figure 8 The changes in nitrogen oxide (including NO, NO2 and N2O) emission concentrations in the exhaust gas of methane-doped ammonia flame combustion under the action of the high-temperature rare earth catalytic functional coating material Y2O3-ZrO2@CeO2 / Tb7O4 / BaO in Example 7 are shown in Figure 7. (a is the NO emission concentration, b is the NO2 emission concentration, and c is the N2O emission concentration.)

[0067] Figure 9 The variation of CO emission concentration in the exhaust gas of methane / air swirl premixed flame combustion with excess air coefficient under different catalytic functional coating thicknesses in Example 7 is shown.

[0068] Figure 10 The NO emission concentration in the exhaust gas of methane / air swirl premixed flame combustion under different catalytic functional coating thicknesses in Example 7 is shown as a function of the excess air coefficient. Detailed implementation method:

[0069] Those skilled in the art will understand that the techniques disclosed in the following embodiments represent those discovered by the inventors that work well in the practice of this invention. However, many changes can be made to the specific embodiments disclosed, still obtaining the same or similar results without departing from the spirit and scope of the invention.

[0070] Example 1

[0071] The high-temperature rare earth composite oxide catalytic functional coating on the wall is a core-shell structured functional material Y2O3-ZrO2@CeO2-Tb7O4-BaO. The core is composed of 80% Y2O3 and 20% ZrO2 by mass, and the outer shell is a rare earth composite oxide CeO2-Tb7O4-BaO, composed of 25% CeO2, 25% Tb7O4 and 50% BaO by mass.

[0072] The preparation steps of rare earth composite oxide particles Y2O3-ZrO2@CeO2-Tb7O4-BaO are as follows:

[0073] 1. Preparation of Y₂O₃-ZrO₂ using Flame Spray Pyrolysis (FSP): First, Zr(NO₃)₄·5H₂O (zirconium nitrate) and Y(NO₃)₃·6H₂O (yttrium nitrate) are dissolved in anhydrous ethanol solution to form a 0.5 mol / L precursor solution. The precursor solution is injected into an external mixing two-phase nozzle at a flow rate of 3 ml / min using a micro-injection pump, where oxygen is broken up under high pressure (5 L / min) to form a precursor spray. The precursor spray is then ignited by an auxiliary ignition flame. Finally, Y₂O₃-ZrO₂ solid solution is formed through processes such as pyrolysis, nucleation, surface growth, condensation, and aggregation. The flow rates of CH₄, O₂, and Ar in the ignition flame gas are 1.25 L / min, 3.2 L / min, and 5.0 L / min.

[0074] 2. CeO2 shell precursor solution Ce(NO3)3·6H2O (cerium nitrate), Tb7O4 shell precursor solution Tb(NO3)3·6H2O (terbium nitrate), and BaO precursor solution Ba(NO3)2 (barium nitrate) are injected downstream of the FSP spray flame. A suitable shell thickness of 50 nm can be obtained by controlling the mixed precursor solution concentration to 0.5 mol / L, maintaining the total flow rate of Ar carrier gas carrying the precursor solutions at 5 L / min, and keeping the injection position 30 cm above the burner outlet.

[0075] The catalytic functional coating material has a rare earth composite oxide Y2O3-ZrO2 core structure; due to the aggregation and chain growth process of nanoparticles synthesized by spray pyrolysis, the final catalyst particles exhibit a network porous structure (e.g., Figure 1 (As shown) The coating wall thickness is approximately 300 μm.

[0076] The specific spraying process is as follows:

[0077] S1, place the core-shell structured functional material Y2O3-ZrO2@CeO2 / Tb7O4 / BaO particles into an oven and dry them at 70℃ for 2 hours.

[0078] S2, the dried core-shell structured functional material Y2O3-ZrO2@CeO2 / Tb7O4 / BaO particles obtained in step S1 are mixed with a 1.3% polyvinyl alcohol solution and mixed in a ball mill for more than 8 hours to obtain a slurry for spray granulation. The slurry is then pumped into a spray drying tower. The outlet temperature in the granulation parameters is set to 105℃~115℃ and the inlet temperature is set to 215℃~225℃ to finally obtain spherical agglomerated powder.

[0079] S3. Before thermal spraying, clean the wall substrate with acetone solution to remove oil stains, then use a corundum abrasive wheel to sandblast and roughen the surface until there is no metallic luster, then clean with alcohol and dry with electric hot air.

[0080] S4. After pretreatment, fix the treated substrate on the workbench, close the vacuum chamber and start evacuating to 0.3 mbar, then introduce argon gas. When the pressure rises to 100 mbar, ignite. After ignition, evacuate the chamber pressure to 80 mbar to preheat the substrate. The preheating temperature is set to 500℃~600℃. After the temperature stabilizes, start spraying the bonding layer NiCoCrAlY. Based on a total mass percentage of 100%, the proportion of each element in the bonding layer NiCoCrAlY is: Cr=20.0%, Co=24.0%, Y=0.76%, Ni=46.14%, Al=9.1%. The particle size requirement for Ni, Cr, and Al is 500 mesh, and the particle size requirement for Y and Co is 200 mesh.

[0081] S5. After the adhesive layer in step S4 is prepared, the sample is subjected to vacuum heat treatment, then the adhesive layer sample is polished with sandpaper, and then placed in alcohol and sonicated for several minutes to maintain the surface roughness below 2μm and the adhesive layer thickness is 50μm to 100μm.

[0082] S6. Fix the processed sample on the stage, close the chamber door, turn on the vacuum system to evacuate to 0.5 mbar, then add argon gas to 40 mbar and ignite the spray gun; then use the vacuum system to evacuate the chamber pressure to 1.5 mbar. The plasma flame will lengthen as the pressure decreases, thus directly preheating the sample to 950℃; when the infrared thermometer detects that the sample surface temperature has reached the set temperature, start powder feeding, and after stabilization, use the atmospheric plasma spraying system for spraying.

[0083] S7. During the spraying process, supply an appropriate amount of oxygen to the vacuum tank to prevent excessive oxygen loss from the crystal structure of the coating material. After reaching the predetermined number of 2 coats, stop the powder feeder and turn off the flame. After the sample cools to room temperature, introduce air, open the chamber, and remove the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO coating material.

[0084] Comparative Example 1:

[0085] Referring to Example 1, the difference is that the Y2O3-ZrO2 solid solution coating material synthesized by flame spray pyrolysis does not have a composite metal oxide shell structure designed on the surface of the Y2O3-ZrO2 particles.

[0086] Comparative Example 2:

[0087] Referring to Example 1, the difference is that an inert metal oxide material, Al2O3 (alumina), is used as the coating material.

[0088] Comparative Example 3:

[0089] The blank control is made of uncoated 304 stainless steel.

[0090] Example 2

[0091] Referring to Example 1, the core of the high-temperature rare earth composite oxide catalytic functional coating material is composed of 80% Y2O3 and 20% ZrO2 by mass. The difference is that the outer shell is a rare earth composite oxide CeO2 / BaO composed of 50% CeO2 and 50% BaO by mass.

[0092] The specific method for synthesizing the rare earth composite oxide particles and the process for spraying them into the burner are described in Example 1.

[0093] Example 3

[0094] Referring to Example 1, the core of the high-temperature rare earth composite oxide catalytic functional coating material is composed of 80% Y2O3 and 20% ZrO2 by mass. The difference is that the outer shell is a rare earth composite oxide La2O3 / BaO, composed of 50% La2O3 and 50% BaO by mass.

[0095] The specific method for synthesizing the rare earth composite oxide particles and the process for spraying them into the burner are described in Example 1.

[0096] Example 4

[0097] Referring to Example 1, the core of the high-temperature rare earth composite oxide catalytic functional coating material is composed of 80% Y2O3 and 20% ZrO2 by mass. The difference is that the outer shell is a rare earth composite oxide Gd2O3 / BaO, composed of 50% Gd2O3 and 50% BaO by mass.

[0098] The specific method for synthesizing the rare earth composite oxide particles and the process for spraying them into the burner are described in Example 1.

[0099] Example 5

[0100] Referring to Example 1, the core of the high-temperature rare earth composite oxide catalytic functional coating material is composed of 80% Y2O3 and 20% ZrO2 by mass. The difference is that the outer shell is a rare earth composite oxide Sc2O3 / BaO, composed of 50% Sc2O3 and 50% BaO by mass.

[0101] The specific method for synthesizing the rare earth composite oxide particles and the process for spraying them into the burner are described in Example 1.

[0102] Example 6

[0103] Referring to Example 1, the core of the high-temperature rare earth composite oxide catalytic functional coating material consists of 80% Y2O3 and 20% ZrO2 by mass. The difference is that the outer shell is a rare earth composite oxide Pr6O. 11 / BaO, composed of 50% Pr6O by mass 11 It consists of 50% BaO by mass.

[0104] The specific method for synthesizing the rare earth composite oxide particles and the process for spraying them into the burner are described in Example 1.

[0105] Example 7: Application of coating materials in burners.

[0106] The wall coating materials of Examples 1-6, Comparative Examples 1 and 2 were applied to rectangular flat plate burners.

[0107] In this embodiment, a rectangular flat-plate burner that simultaneously achieves combustion enhancement and nitrogen oxide degradation based on a high-temperature rare-earth catalytic functional coating material comprises a combustion system consisting of a detachable plate-type square wall, heating plates, a flat flame burner, a movable fixed bracket, a wall-mounted temperature-controlled heater, a ceramic heat-insulating base, and a high-temperature resistant fused silica window. The slit distance between the two heating plates is controlled by a micrometer adjustment system. The micrometer is connected to the fixed bracket, and the heating plates are fixed on a slide rail perpendicular to the micrometer's axis. When the slider moves forward, the axial distance of the micrometer is the lateral distance of the heating plate. The micrometer has an accuracy of 0.01 mm. To adjust the contact area between the combustion flame and the catalytic functional coating wall, the controllable distance between the two heating plates ranges from 2 mm to 20 mm. To adjust the chemical effect intensity of the catalytic functional coating, the heating temperature range of the coating wall is 100℃ to 1000℃.

[0108] During normal operation of the rectangular flat plate burner, a premixed gas of hydrocarbon fuel and air is injected from the flat flame burner, and after ignition, a stable combustion flame is formed in the rectangular flat plate burner.

[0109] The test conditions, combustion stability, and nitrogen oxide emissions are as follows:

[0110] Operating Condition 1: The fuel is a premixed gas of methane and air, the fuel flow rate is 1.5 m / s, the premixed gas equivalence ratio is 1.0, and the wall temperature is 300–800 °C. The wall coatings are Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material (Example 1), Y2O3-ZrO2 solid solution material (Comparative Example 1), and Al2O3 material (Comparative Example 2), respectively. The measurement results of the minimum channel spacing (i.e., the flame quenching spacing) that can maintain stable flame propagation in the flat plate channel under different wall temperature conditions are as follows: Figure 3 As shown.

[0111] Operating Condition 2: The fuel is a premixed gas of methane and air, with a fuel flow rate of 1.5 m / s, a premixed gas equivalence ratio of 0.9–1.2, a flat plate channel spacing of 4 mm, and a wall temperature of 800 °C. The wall coatings used are Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material (Example 1), Y2O3-ZrO2 solid solution material (Comparative Example 1), and Al2O3 material (Comparative Example 2). The comparison results of NO emission concentration (calculated based on an oxygen content of 3.5%) in the combustion exhaust gas under different premixed gas equivalence ratios are as follows: Figure 4 As shown.

[0112] Operating Condition 3: The fuel is a premixed gas of methane and air, the fuel flow rate is 1.5 m / s, the premixed gas equivalence ratio is 0.9, the wall temperature is 800℃, and the wall coating uses the core-shell materials of Examples 1-5 and Comparative Example 1, respectively. The comparison results of the critical flameout distance and NO emission concentration (calculated based on an oxygen content of 3.5%) under the action of different shell structure coating materials are as follows: Figure 5 As shown in the figure. The NO emission concentration changes with different operating times, the results are as follows. Figure 6 As shown.

[0113] Operating Condition 4: The fuel is a premixed gas of methane, ammonia, and air, with an ammonia blending rate of 10%. The fuel flow rate is 1.5 m / s, the global equivalence ratio of the premixed gas is 1.0, the flat plate channel spacing is 12 mm and 5 mm, and the wall temperature is 700 °C. The wall surface is coated with Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material (Example 1) and uncoated 304 stainless steel material (Comparative Example 3), respectively. The comparison results of the flame center temperature at different height positions along the streamline direction are as follows: Figure 7 As shown.

[0114] Operating Condition 5: The fuel is a premixed gas of methane, ammonia, and air, with ammonia blending amounts of 0%, 10%, 20%, 30%, and 40%. The fuel flow rate is 1.5 m / s, the global equivalence ratio of the premixed gas is 0.9–1.2, the flat plate channel spacing is 4 mm, and the wall temperature is 700 °C. The wall surface is coated with Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material (Example 1) and uncoated 304 stainless steel (Comparative Example 3), respectively. The comparison results of the emission concentrations of pollutants NO, NO2, and N2O in the combustion exhaust gas (calculated based on an oxygen content of 3.5%) under different equivalence ratios are as follows: Figure 8 As shown.

[0115] Operating Condition 6: A swirling premixed gas of methane and air is used as fuel. The combustion heat load is 2kW, the excess air coefficient ranges from 0.9 to 1.4, the flat plate channel spacing is 20mm, the wall temperature is 300℃, and the wall surface uses a Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material coating with thicknesses of 300μm, 400μm, 500μm, and 600μm. The comparison results of CO and NO emission concentrations (converted to 3.5% oxygen content) in the combustion exhaust gas under different excess air coefficient conditions are as follows: Figure 9 and Figure 10 As shown.

[0116] Basicity has a significant impact on the catalytic effect of catalysts. In catalytic reactions, the surface properties of the catalyst play a crucial role in the reaction rate and selectivity. Basicity can affect the charge distribution of the active sites on the catalyst and the adsorption of reactant molecules, thus influencing the catalytic reaction. Specifically, basicity can affect the acid-base properties of the catalyst surface, altering the electron distribution of active sites and the adsorption of reactant molecules on the surface. Appropriate basicity conditions can favor certain catalytic reactions. Excessively high or low basicity can affect the catalyst activity, leading to reduced catalytic efficiency or even catalytic failure. Therefore, it is necessary to select materials with high activity, such as BaO (barium oxide), CuO (copper oxide), Gd₂O₃ (gadolinium oxide), Tb₇O₄ (terbium oxide), Sc₂O₃ (scandium oxide), and Pr₆O₃. 11 Praseodymium oxide can be used as a catalyst outer shell.

[0117] from Figure 3 and Figure 4The experimental results show that, compared with the inert Al2O3 coating material wall surface (Comparative Example 2), the Y2O3-ZrO2 solid solution material coating used in Comparative Example 1 and the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material coating used in Example 1 can significantly reduce the critical quenching distance of the methane / air premixed flame under different wall surface temperature conditions, thus achieving the purpose of combustion catalytic enhancement, especially the latter high-temperature rare earth loaded oxide catalytic functional coating. Meanwhile, the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material coating used in Example 1 can significantly reduce the NO emission concentration of the methane / air premixed flame combustion pollutant under different equivalence ratio conditions, with the highest NO emission concentration still below 30 ppm, achieving the goal of ultra-low nitrogen oxide emissions.

[0118] from Figure 5 The experimental results show that, by comparing the wall surfaces of the five shell-structured coating materials (Examples 2-6) with the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell coating used in Example 1 under the same operating condition of 800 degrees Celsius and an equivalence ratio of 0.9, it is evident that each shell structure exhibits significantly better flameout distance and NO emission concentration in a methane / air premixed flame, achieving both enhanced combustion and catalytic purification of combustion exhaust gases. Meanwhile, the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell coating used in Example 1 demonstrates significantly better flameout distance and NO emission concentration than the five shell-structured coating materials in Examples 2-6 under the same operating condition, with the lowest flameout distance below 1.0 mm and the lowest NO emission concentration below 22 ppm, achieving the goal of ultra-low nitrogen oxide emissions.

[0119] The technical principle of the high-temperature rare earth catalytic functional coating synergistically controlling combustion enhancement and nitrogen oxide reduction proposed in this invention is as follows: Figure 1 As shown. During normal operation of the rectangular flat-plate burner, a premixed gas of hydrocarbon fuel and air is injected from the flat-flame burner, and a stable combustion flame is formed inside the rectangular flat-plate burner after ignition. Taking the (Y2O3-ZrO2)@CeO2 / Tb7O4 / BaO core-shell structure catalyst of Example 1 as an example, the high-temperature flame and the rare earth catalytic functional coating material are in full contact inside the rectangular flat-plate burner. Under the dual effects of high-temperature flame and high-temperature wall heating, the stretching vibration and charge transport speed between atoms inside the rare earth functional coating material are accelerated, promoting the migration of oxygen from the bulk lattice of the metal oxide to the surface. On the one hand, more active oxygen species are released to participate in the gas-phase chain chemical reaction; on the other hand, the generated oxygen vacancies can quickly adsorb, decompose, and desorb the combustion product NOx molecules; thus, the chemical effects of the functional coating in catalytic oxidation of CxHy and catalytic reduction of NOx are enhanced.

[0120] from Figure 6 The durability test results show that, compared with the uncoated blank wall surface, the NO emission concentration of the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material coating remained stable after 6 hours, while the NO emission concentration of the blank wall surface increased with time. This result demonstrates that the wall surface coated with the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material exhibits a stable trend, verifying its stability and reliability.

[0121] from Figure 7 and Figure 8 The experimental results show that, compared with the uncoated blank wall surface, the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material coating can significantly increase the combustion temperature in the central streamline direction of the methane-ammonia-blended flame, especially when used in burners with a smaller plate channel spacing of 5mm, where the combustion enhancement effect is even more pronounced. Simultaneously, the Y2O3-ZrO2@CeO2 / Tb7O4 / BaO core-shell material coating can significantly reduce the emission concentration of nitrogen oxides (including NO, NO2, and N2O) in the exhaust gas of the methane-ammonia-blended flame, achieving a synergistic control effect of combustion enhancement and nitrogen oxide degradation.

[0122] from Figure 9 and Figure 10 Experimental test results show that the high-temperature rare earth composite oxide catalytic functional coating material Y2O3-ZrO2@CeO2 / Tb7O4 / BaO can still simultaneously achieve combustion enhancement and nitrogen oxide reduction in a swirling, high-power methane / air premixed burner, realizing efficient and clean combustion. Furthermore, the coating thickness on the wall surface significantly affects the catalytic effect. With increasing coating thickness, the emission concentrations of CO and NO in the combustion exhaust gas both show an increasing trend, especially under operating conditions with a high excess air coefficient.

Claims

1. A high-temperature rare earth composite oxide catalytic functional coating, characterized in that, The coating is applied inside the burner, and the coating material is a core-shell structured functional material Y2O3-ZrO2@M x O y Using Y2O3-ZrO2 solid solution material as the core structure, with M x O y The additive material has a shell structure; M x O y The auxiliary materials include rare earth metal oxides and alkaline earth metal oxides; based on a total mass percentage of 100%, the Y2O3-ZrO2 solid solution material comprises 70-80% Y2O3 and 20-30% ZrO2 by mass; based on a total mass percentage of 100%, the M... x O y The additive materials include 45-55% by mass of rare earth metal oxides and 45-55% by mass of alkaline earth metal oxides; the rare earth metal oxides are CeO2, La2O3, Gd2O3, Tb7O4, Sc2O3, and Pr6O. 11 The alkaline earth metal oxide is BaO, which is any one or more of the following: The preparation method of the Y2O3-ZrO2 solid solution material adopts the flame spray pyrolysis method, and the specific steps are as follows: First, Zr(NO3)4·5H2O and Y(NO3)3·6H2O are dissolved in anhydrous ethanol solution to form a precursor solution of 0.5-0.7 mol / L; The precursor solution is injected into an externally mixed two-phase nozzle via a micro-injection pump at a flow rate of 3-4 ml / min. Under high pressure, oxygen is broken up to form a precursor spray at a flow rate of 5-7 L / min. The precursor spray is then ignited by an auxiliary ignition flame at a flow rate of 1.25-1.5 L / min for CH4, 3.2-3.5 L / min for O2, and 5.0-6.0 L / min for Ar. Finally, through pyrolysis, nucleation, surface growth, condensation, and aggregation, a Y2O3-ZrO2 solid solution is formed. This results in the core-shell structured functional material Y2O3-ZrO2@M x O y The preparation method is as follows: Y2O3-ZrO2 solid solution material is prepared by flame spray pyrolysis, and then M is sprayed downstream of the FSP spray flame. x O y The shell precursor solution is controlled at a concentration of 0.5-0.7 mol / L, and the total flow rate of the carrier gas Ar carrying the precursor solution is maintained at 5 L / min. The injection position is 30 cm above the burner to control the shell thickness at 5-50 nm.

2. The high-temperature rare earth composite oxide catalytic functional coating according to claim 1, characterized in that, Based on a total mass percentage of 100%, the M x O y The auxiliary materials include CeO2 with a mass fraction of 20-25%, Tb7O4 with a mass fraction of 20-25%, and BaO with a mass fraction of 50-60%.

3. The high-temperature rare earth composite oxide catalytic functional coating according to claim 1, characterized in that, The coating thickness is 300μm~600μm.

4. The method for preparing the high-temperature rare earth composite oxide catalytic functional coating according to any one of claims 1 to 3, characterized in that, Includes the following steps: Core-shell functional material Y2O3-ZrO2@M x O y After drying, the mixture is ball-milled with a polyvinyl alcohol solution and pumped into a spray drying tower to prepare spherical agglomerated powder. After cleaning the substrate wall, a NiCoCrAlY adhesive layer is sprayed on. Then, after vacuum heat treatment, the powder is fed under vacuum at high temperature and sprayed using an atmospheric plasma spraying system.

5. The method according to claim 4, characterized in that, Specifically, the following steps are included: S1, using core-shell structured functional materials Y2O3-ZrO2@M x O y Place in an oven to dry at a temperature of 70℃~120℃ for 2-4 hours; S2, the dried core-shell functional material Y2O3-ZrO2@M obtained in step S1 x O y The particles are mixed with a 1-5% polyvinyl alcohol solution and mixed in a ball mill for 8-10 hours or more to obtain a slurry for spray granulation. The slurry is then pumped into a spray drying tower. The outlet temperature in the granulation parameters is set to 105℃~115℃ and the inlet temperature is set to 215℃~225℃ to finally obtain spherical agglomerated powder. S3. Before thermal spraying, clean the wall substrate with acetone solution to remove oil stains, then use a corundum abrasive wheel to sandblast and roughen the surface until there is no metallic luster, then clean with alcohol and dry with electric hot air. S4. After pretreatment, fix the treated substrate on the worktable, close the vacuum chamber and start evacuating to 0.3-0.5 mbar, then introduce argon gas. When the pressure rises to 100-120 mbar, ignite the gas. After ignition, reduce the chamber pressure to 80-100 mbar to preheat the substrate. The preheating temperature is set to 500℃~600℃. After the temperature stabilizes, start spraying the NiCoCrAlY adhesive layer. Based on a total mass percentage of 100%, the element ratio in the NiCoCrAlY adhesive layer is: Cr=20.0%, Co=24.0%, Y=0.76%, Ni=46.14%, Al=9.1%. S5. After the adhesive layer in step S4 is prepared, the sample is subjected to vacuum heat treatment, then the adhesive layer sample is polished with sandpaper, and then placed in alcohol and sonicated for several minutes to maintain the surface roughness below 2μm and the adhesive layer thickness is 50μm~100μm. S6. Fix the processed sample on the stage, close the chamber door, turn on the vacuum system, add argon gas and then ignite the spray gun; adjust the chamber pressure and preheat the sample directly; when the infrared thermometer detects that the sample surface temperature has reached the set temperature, start feeding powder, and after stabilization, use the atmospheric plasma spraying system for spraying. S7. During the spraying process, oxygen is supplied to the vacuum chamber to prevent excessive oxygen loss from the crystal structure of the coating material. After spraying 2-4 times, the powder feeder is stopped and the flame is turned off. After the sample has cooled to room temperature, air is introduced to open the chamber and remove Y2O3-ZrO2@M. x O y Coating materials.

6. The method according to claim 5, characterized in that, In step S2, the dried core-shell structured functional material Y2O3-ZrO2@M x O y The solid-liquid mass ratio of the particles to the polyvinyl alcohol solution is 0.8-1:1.2-1.5; in step S6, the vacuum system is turned on to evacuate to 0.5-0.8 mbar, argon gas is added to 40-45 mbar and then the spray gun is ignited, the chamber pressure is adjusted to 1.5-2 mbar, and the sample preheating temperature is 950-1000℃.

7. The application of the high-temperature rare earth composite oxide catalytic functional coating according to any one of claims 1 to 3 in a burner, characterized in that, Different catalytic functional coating modules are designed and arranged inside the burner, including wall coating, integral honeycomb, porous medium heat storage body, and solid sintered sleeve; the catalytic functional coating modules are designed as integral or split structures in the form of rectangles, squares, and cylinders according to the geometry of the burner.

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