Silicon dioxide coating supported catalyst with high thermal stability and preparation method thereof

Abstract

The invention discloses a silicon dioxide coating supported catalyst with high thermal stability and a preparation method of the silicon dioxide coating supported catalyst, belongs to the technical field of heterogeneous catalyst preparation, and particularly relates to an anti-sintering catalyst for inhibiting high-temperature sintering by constructing a porous silicon dioxide coating on the surface and a preparation method of the anti-sintering catalyst. The catalyst is mainly applied to petrochemical engineering and other catalytic reaction fields requiring high temperature or severe atmosphere. The method at least comprises the following steps: loading active metal on the surface of a catalyst carrier and reducing the active metal. Then, the silicon dioxide is placed in a mixed solution of ethyl alcohol and ammonia water, an ethyl alcohol solution of tetraethyl orthosilicate is slowly injected at a constant speed under continuous stirring, and a silicon dioxide coating reaction is carried out; and after the reaction is finished, filtering, washing and drying, and calcining and chambering in an air environment at 300-500 DEG C to obtain the catalyst. On the premise of controlling the cost, the thermal stability and the catalytic life of the catalyst under a high-temperature condition are remarkably improved, and the key problem that the catalyst is inactivated due to high-temperature sintering is solved.

Description

Technical Field

[0001] This invention belongs to the field of multiphase catalyst preparation technology, specifically relating to a supported catalyst with high thermal stability and its preparation method, particularly to an anti-sintering catalyst and its preparation method by constructing a porous silica coating on the surface to suppress high-temperature sintering. Background Technology

[0002] Supported metal catalysts are widely used in petrochemicals, automotive exhaust purification, energy conversion (such as methane reforming and Fischer-Tropsch synthesis), and fine chemical synthesis. These catalysts typically disperse active metal components (such as noble metals like Pt, Pd, Rh, and Au, or transition metals like Ni, Co, and Cu) as nanoparticles on a support with a large specific surface area (such as Al₂O₃, SiO₂, TiO₂, and carbon materials). The high dispersion of metal nanoparticles exposes more surface active sites, thereby significantly improving catalytic efficiency.

[0003] However, in practical industrial applications, many catalytic reactions need to be carried out at high temperatures (typically above 400°C, even exceeding 800°C) or under harsh oxidizing / reducing atmospheres. According to thermodynamic principles, nanoscale metal particles possess extremely high surface energy and are in a metastable state. Under high-temperature driving conditions, metal nanoparticles are highly susceptible to sintering.

[0004] Sintering mainly occurs through two mechanisms: Ostwald ripening: Atoms or molecules detach from the surface of smaller particles, migrate through gas phase or surface diffusion, and deposit onto larger particles, resulting in a "big eats small" phenomenon.

[0005] Particle migration and coalescence: The entire nanoparticle moves on the surface of the carrier, and when two particles meet, they merge into a larger particle.

[0006] Sintering leads to a sharp increase in metal particle size and a significant decrease in the active specific surface area, resulting in irreversible degradation of catalyst activity and severely shortening its lifespan. Therefore, how to improve the anti-sintering ability of metal catalysts while maintaining high dispersion is a core scientific problem that urgently needs to be solved in the field of catalysis.

[0007] To improve the high-temperature stability of supported catalysts, existing technical approaches mainly focus on the following aspects: (1) Enhanced metal-support interaction This strategy utilizes the strong interaction between reducible oxide supports (such as TiO2, CeO2, Nb2O5, etc.) and metal particles to anchor the metal particles. Under high-temperature reducing conditions, support species may migrate to the surface of the metal particles to form a modification layer, thereby physically inhibiting the movement of the metal particles. However, although the SMSI effect can significantly improve anti-sintering performance, it is often accompanied by a loss of activity. This is because the coating layer formed by the migration of the support can mask some active sites, hindering the adsorption of reactant molecules. In addition, this method has strict limitations on the choice of support; for widely used inert supports (such as α-Al2O3, SiO2) or carbon supports, it is difficult to achieve strong anchoring through the simple SMSI effect.

[0008] (2) Channel confinement strategy This method involves encapsulating metal nanoparticles within the pores of mesoporous materials (such as SBA-15, MCM-41) or microporous materials (such as zeolite molecular sieves, MOFs). The physical barrier effect of the pore walls restricts the migration and aggregation of the metal particles. However, the confinement of these pores is limited by the thermal stability of the support framework itself. For example, many ordered mesoporous silicas undergo framework collapse at extremely high temperatures. More importantly, placing metal particles within deep pores introduces significant internal diffusion resistance, leading to limited reaction rates. This strategy is often counterproductive, especially for systems involving macromolecular reactants.

[0009] (3) Surface coating / core-shell structure encapsulation technology This is currently the most direct and effective anti-sintering strategy, and also a research hotspot in this field. Its core idea is to deposit a physical barrier (usually a porous oxide such as SiO2, Al2O3, or ZrO2) on the surface of the supported catalyst, constructing a "core-shell" or "yolk-shell" structure to physically isolate metal particles and prevent them from contacting and agglomerating. Among these, silica (SiO2) is the most commonly used coating material due to its good chemical inertness, thermal stability, and easily adjustable porosity. However, existing silica coating technologies have significant technical bottlenecks: while atomic layer deposition (ALD) can achieve precise atomic-level control and grow ultrathin oxide films of uniform thickness on the catalyst surface, its equipment is expensive, precursor costs are high, deposition rates are slow, and it typically requires a high vacuum environment, making it difficult to process powder catalysts on an industrial scale. While traditional wet chemical methods offer a lower-cost approach, they are difficult to precisely control the thickness and porosity of the coating layer, often resulting in a thicker silica layer. This not only increases mass transfer resistance but may also completely bury active sites.

[0010] In summary, although significant progress has been made in the research of anti-sintering catalysts, there remains an irreconcilable contradiction between "stability" and "activity".

[0011] In particular, regarding silica coating technology, there is currently a lack of a technology on the market that can achieve large-scale preparation through a simple, low-cost wet chemical method while precisely controlling the coating to be "ultra-thin" and "porous." That is, how to construct a "smart" protective film on the catalyst surface without relying on expensive ALD equipment—a film that can physically isolate and prevent sintering while being thin enough to allow reactants to move rapidly—is a key technical challenge that urgently needs to be solved in the field of catalyst preparation engineering. This is precisely the core technical problem that this invention aims to solve. Summary of the Invention

[0012] In view of this, the purpose of this invention is to provide a highly thermally stable silica-coated supported catalyst and its preparation method, which is safe, reliable, and produces minimal pollution. A silicon source generated by the hydrolysis of tetraethyl orthosilicate in an alkaline solution is uniformly deposited on the surface of the supported catalyst to form a silica film of controllable thickness. This restricts the migration and sintering of active sites on the catalyst surface, increasing the thermal stability of the catalyst in high-temperature environments. This results in a long-life catalyst suitable for commercial application.

[0013] The preparation process of this invention achieves ultrathin and uniform silica coating on the surface of supported catalysts under a wet chemical environment by precisely controlling chemical kinetics, thus resolving the contradiction between catalyst thermal stability and catalytic activity. Furthermore, this method is simple, low-cost, and allows for large-scale preparation of highly thermally stable supported catalysts, improving the lifespan of commercial catalysts.

[0014] To achieve the above objectives, the catalyst preparation technique includes the following steps: (1) Load the active sites of the catalyst onto the surface of the catalyst support and reduce the active sites into metal particles to obtain a supported catalyst.

[0015] Furthermore, the catalyst support mentioned in step (1) can be an oxide support, a two-dimensional material support, a metal nanocluster, or a molecular sieve. The active sites can be loaded using methods such as impregnation, precipitation, sol-gel, hydrothermal synthesis, chemical bonding, mixing, ion exchange, melting, chemical vapor deposition, plasma flame, and Joule heating. The reduction methods for the active sites can be thermal reduction under a reducing atmosphere, plasma reduction, photochemical reduction, electrochemical reduction, biological reduction, and liquid-phase reduction.

[0016] (2) Mix the solutions of ethanol and concentrated ammonia, and denote them as solution A. Put the supported catalyst into solution A and stir to form a suspension.

[0017] Further, in step (2), the ratio of ethanol to concentrated ammonia in solution A is 1:10 to 1:30, and the ammonia concentration of concentrated ammonia is 20%-30%.

[0018] (3) Mix tetraethyl orthosilicate (TEOS) solution with ethanol solution, and denote it as solution B. While stirring continuously, inject solution B into solution A at a certain speed. Furthermore, in step (3), the ratio of the mass of tetraethyl orthosilicate in solution B to the total surface area of ​​the supported catalyst is 10-100 mg / m². 2 The volume ratio of the ethanol solution to the volume of solution A is 0.25-0.5, the stirring speed is 100-1000 r / min, and the injection rate of the solution is 10-100 μl / min.

[0019] (4) After stirring the mixture of solutions A and B for a certain period of time, collect and wash the particulate matter in the mixture. Further, the stirring time in step (4) is to continue stirring for 0-12 hours at the stirring speed in step (3) after the solution is injected. The method for collecting the particulate matter in the solution can be filtration, vacuum filtration, static precipitation, centrifugation or high-temperature drying of the solution. The washing solution can be deionized water or ethanol solution.

[0020] (5) The washed filter material is dried and calcined in air. After calcination, the sample is naturally cooled at room temperature to finally obtain the high thermal stability silica-coated supported catalyst.

[0021] Furthermore, the drying temperature in step (5) can be 40-120 degrees Celsius, and the drying time can be 1-12 hours. For calcination in an air environment, the catalyst needs to be placed in a heating device and heated to 300-500 degrees Celsius at a heating rate of 0.5-2°C / min in an air atmosphere, and then kept at that temperature for 1-12 hours.

[0022] Compared with the prior art, the advantages of the present invention are: 1. This invention overcomes the limitations of traditional wet chemical methods' "homogeneous nucleation," achieving nanoscale precise control of coating thickness. In existing technologies using TEOS for coating, the high local concentration often leads to rapid hydrolysis and condensation of TEOS in the bulk solution, resulting in homogeneous nucleation and the formation of free silica microspheres, rather than a coating growing on the catalyst surface. This results in low coating efficiency, and requires increasing the feed rate to cover the catalyst, ultimately leading to an excessively thick coating. This invention controls the injection of solution B at an extremely low rate of 10-100 μl / min, and uses a specific ratio of tetraethyl orthosilicate to the catalyst surface area (10-100 mg / m²). 2 This creates a "starved feed" reaction environment.

[0023] Kinetic advantage: This feeding method consistently keeps the silicon source concentration in the reaction system below the critical supersaturation. According to the LaMer nucleation theory, the system cannot provide enough energy to overcome the homogeneous nucleation barrier at this point. The silicon precursor generated by TEOS hydrolysis preferentially adsorbs onto the surface of a supported catalyst with higher surface energy for heterogeneous nucleation.

[0024] Furthermore, due to the suppression of free byproduct formation, the utilization rate of the silicon source is close to 100%. The inventors can precisely adjust the thickness of the silica coating within the range of 1-20 nm by simply adjusting the total amount of TEOS added (the mass ratio described in claim 5). This precision was previously only achievable with expensive ALD technology, but this invention can achieve it through a simple wet chemical method, greatly lowering the preparation threshold.

[0025] 2. This invention solves the trade-off between "anti-sintering" and "high activity," constructing a selectively permeable structure. Traditional coating techniques often result in reactants being unable to contact the internal active sites due to dense or excessively thick coatings, significantly reducing catalytic efficiency. The catalyst prepared in this invention perfectly balances stability and activity. Physical confinement and thermal stability: The silica coating formed by this invention acts like a robust "armor," physically anchoring the metal nanoparticles to the carrier. Under high-temperature reaction conditions (300-500°C or even higher as mentioned in claim 7), this coating effectively blocks the migration path of metal particles, inhibits Ostwald ripening and particle aggregation, significantly improves the catalyst's resistance to sintering, and extends its service life.

[0026] In-situ pore formation and mass transfer optimization: A key step in this invention lies in the combination of a specific calcination process. During preparation, the ethanol and ammonia environment results in a silica gel network containing a large number of ethoxy groups and solvent molecules. In the subsequent air calcination, these organic groups decompose and the solvent evaporates, leaving abundant micropores and mesopores in the dense silica shell. These pores are large enough to allow small molecules of conventional reactants (such as hydrogen, oxygen, carbon monoxide, ethylene, etc.) to freely pass through and reach the internal active sites, while metal particles (typically larger) are firmly locked inside the shell. This sieving structure both preserves intrinsic activity and provides protection.

[0027] 3. The process is highly versatile and applicable to various carrier and active component systems. Unlike chemical methods that require specific functional groups for deposition, this invention utilizes the principles of physical adsorption and surface hydrolysis condensation.

[0028] Support diversity: As described in claim 2, this method is applicable not only to traditional oxide supports (such as alumina and titanium dioxide), but also to two-dimensional materials with vastly different surface properties (such as graphene), metal nanoclusters, and even molecular sieves. This means that the technology has platform technology attributes and can be widely applied in various catalytic fields such as hydrogenation, oxidation, and reforming.

[0029] Active site protection: This invention employs a "reduction first, coating later" strategy. This avoids the segregation and secondary dispersion of the metal precursor during the coating process that may occur with the "coating first, reduction later" method in traditional approaches. The metal particles directly contact the silica precursor, forming Si-OM bonds at the interface, further enhancing the metal-support interaction (SMSI).

[0030] 4. Significant industrial application potential and cost advantages. Low cost: Compared to the ultra-high vacuum equipment and expensive organometallic precursors required for atomic layer deposition (ALD), this invention only requires conventional reaction vessels and stirrers, using inexpensive and readily available ethanol, ammonia, and TEOS as raw materials. Easy scale-up: The process parameters (stirring speed, mixing ratio) set in this invention are all within the range of conventional industrial operations. In particular, the strategy of adjusting coating quality by controlling the dropping speed can be easily automated in industrial production using metering pumps, possessing extremely high potential for scale-up to the hundreds of kilograms or even tons. Environmentally friendly: The solvent system mainly consists of ethanol and water; the amount of ammonia used is controllable and can be volatilized or recovered during the drying and calcination process, leaving no heavy metal residues and meeting the requirements of green chemistry production.

[0031] 5. Tunerability and Multifunctionality of Catalyst Surface Properties. According to claim 10, the catalyst obtained by this invention is not only a physical complex, but also a chemically modifiable system: Acidic Site Regulation: By controlling the calcination temperature and time, the number of silanol groups (Si-OH) retained on the silica shell surface can be adjusted. These silanol groups not only provide the ability to regulate hydrophilic / hydrophobic properties, but can also participate in the reaction as weakly acidic sites, or serve as anchors for subsequent grafting of other functional molecules (such as organic ligands). Electronic Property Regulation: The ultrathin silica layer is in close contact with the internal metal particles, and high-temperature treatment often induces electron transfer, changing the electron cloud density of the metal active center, thereby optimizing its adsorption energy for the reaction substrate. This makes the catalyst not only more stable, but in some structure-sensitive reactions, its intrinsic activity (TOF) is even superior to that of the uncoated bare catalyst.

[0032] 6. Unique coating structure stability In the preparation process of this invention, prolonged stirring (0-12 hours as described in claim 6) and subsequent heat treatment ensure complete hydrolysis and condensation of the silica precursor. The resulting SiO2 network structure exhibits high cross-linking degree and strong structural rigidity. Experiments show that the catalyst prepared using the method of this invention retains its silica shell intact after undergoing high temperature, redox cycles, and even hydrothermal treatment, without cracking or detachment. This excellent mechanical and thermal stability makes the catalyst particularly suitable for harsh conditions such as automotive exhaust treatment and high-temperature propane dehydrogenation.

[0033] In summary, this invention successfully solves the sintering deactivation problem commonly faced by supported catalysts through a simple, economical, and highly controllable wet chemistry strategy. This technology achieves a precise coating effect similar to ALD technology without requiring expensive equipment, and retains catalytic activity through in-situ pore formation. It is a general-purpose catalyst preparation platform technology with extremely high academic value and promising industrial applications. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the method for preparing the silica-coated supported catalyst of the present invention.

[0035] Figure 2 This is a TEM image of the silica-coated supported catalyst prepared in Example 1 of the present invention.

[0036] Figure 3 The images show TEM images and particle size statistics of the silica-coated supported catalyst prepared in Example 1 of this invention before and after the reaction, 10 hours later.

[0037] Figure 4The images show TEM images and particle size statistics of the silica-coated supported catalyst prepared in Comparative Example 1 of this invention before and after the reaction.

[0038] Figure 5 The reaction conversion rate of the catalysts prepared in Example 1 and Comparative Example 1 of this invention changes with reaction time over 10 hours. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0040] Unless otherwise stated, the solution composition in this invention should be as simple and free of impurities as possible. Preferably, the reagents used in this invention can be commercially available analytical grade reagents.

[0041] In this invention, the solution ratio and carrier surface structure need to be adjusted through certain experiments. The specific data can be determined according to the desired thickness and morphology of the silica coating.

[0042] The steps for preparing a silica-coated supported catalyst with high thermal stability are as follows: A supported catalyst is prepared and the active sites are reduced to nano-metal particles. The well-dispersed supported catalyst is dispersed in a mixed solution of anhydrous ethanol and concentrated ammonia, and stirred at high speed to form a homogeneous suspension, ensuring uniform catalyst dispersion. A calculated amount of tetraethyl orthosilicate (TEOS) is dissolved in anhydrous ethanol, and the TEOS solution is slowly added dropwise to the suspension using a micro-pump, while the suspension is continuously stirred to allow the silane precursor to adsorb onto the catalyst surface and form a coating structure. After the addition is complete, stirring continues, utilizing the catalytic effect of the alkaline environment to initiate the hydrolysis and condensation of the silane precursor on the catalyst surface. After the reaction is complete, the suspension is filtered, dried, and calcined in air to create pores. Finally, it is treated under a reducing atmosphere to obtain the final catalyst. Example

[0043] In this embodiment, the PtSn alloy was prepared on a silica support surface, and the ratio of the silica coating mass to the catalyst surface area was 20 mg / m². 2 High thermal stability supported catalyst.

[0044] The first step involved dissolving 0.05 g of chloroplatinic acid and stannous chloride (atomic ratio 1:1) in 4 ml of hydrochloric acid solution (concentration 32%) to form a PtSn complex hydrochloric acid solution. This solution was then slowly added dropwise to the surface of a 1 g mesoporous silica support, allowing for uniform absorption. The PtSn complex-loaded silica was then dried in an 80°C oven for 12 hours, followed by transfer to a muffle furnace. A hydrogen-to-nitrogen gas ratio of 1:9 was introduced at a flow rate of 300 ml / min, while the temperature was gradually increased from 30°C to 400°C at a rate of 1°C / min. This temperature was maintained for 1 hour, after which the hydrogen flow was stopped, and the furnace was allowed to cool naturally to room temperature, yielding the supported catalyst PtSn / SiO2.

[0045] The second step involves weighing 0.2 g of the prepared supported catalyst PtSn / SiO2 and placing it in a round-bottom flask. A solution A, consisting of 70 ml of anhydrous ethanol and 3.5 ml of concentrated ammonia (NH3·H2O concentration of 28%), is then added. The solution is stirred at 600 r / min using a magnetic stirrer to ensure the catalyst powder is evenly dispersed in the solution, forming a suspension.

[0046] Third, according to the target coating amount, weigh 34.7 mg of tetraethyl orthosilicate and dissolve it in 35 ml of anhydrous ethanol. Mix them evenly to form solution B. While keeping the suspension continuously stirred, use a micro-injection pump to slowly add solution B dropwise to solution A at a constant rate of 0.04 ml / min.

[0047] Fourth step: After solution B is added, keep the reaction system at room temperature and continue stirring for 10 hours to ensure that tetraethyl orthosilicate is fully hydrolyzed and deposited on the PtSn / SiO2 surface.

[0048] In the fifth step, after the reaction was complete, the solid product was collected by vacuum filtration and washed three times with ethanol to remove residual impurities on the surface. The filter cake was then placed in an oven and dried at 105°C for 12 hours. Subsequently, the dried powder was placed in a tube furnace and calcined in air. The temperature program was set to slowly increase to 350°C at a rate of 1°C / min and calcined at this temperature for 2 hours to ensure the removal of the organic template and the formation of a porous silica layer.

[0049] Step 6: After calcination, the sample is cooled to room temperature. Then, a mixture of hydrogen and nitrogen in a ratio of 1:9 is introduced and the temperature is gradually increased to 400°C at a rate of 5°C / min. After maintaining the temperature for 1 hour, the flow of hydrogen is stopped, and the furnace temperature is allowed to cool naturally to room temperature to obtain a supported catalyst Si@PtSn / SiO2 with high thermal stability and silicon coating.

[0050] The catalyst obtained in this example was measured.

[0051] Comparative Example 1 To verify the anti-sintering effect of the present invention, Comparative Example 1 was set up. 0.2g of PtSn / SiO2 catalyst was taken and the sample without step (2-5) was recorded as PtSn / SiO2 catalyst and used as blank control group to evaluate the state of unprotected catalyst after high temperature treatment.

[0052] The catalyst obtained in this comparative example was measured.

[0053] Carbon dioxide-assisted propane dehydrogenation experiments were conducted on the catalysts of this embodiment and the comparative example. The reaction temperature was 580 degrees Celsius, the feed conditions were C3H8:CO2:N2=1:1:2, the total feed rate was 20 ml / min, and the reaction time was 10 hours.

[0054] Figure 2 The image shows a TEM image of the catalyst prepared in Example 1 of this invention before the reaction. As can be seen from the image, a SiO2 coating layer with a thickness of about 2-3 nm appeared on the surface of the catalyst nano-alloy particles.

[0055] Figure 3 (ab) shows the TEM image and particle size distribution of the catalyst prepared in Example 1 of this invention before the reaction. Figure 3 (cd) is a TEM image of the catalyst prepared in Example 1 of the present invention after reacting at 580 degrees for 10 hours. As can be seen from the figure, the nano-alloy particles of the catalyst in Example 1 did not show obvious sintering phenomenon during the reaction.

[0056] Figure 4 (ab) shows the TEM image and particle size distribution of the catalyst prepared in Comparative Example 1 of this invention before the reaction. Figure 4 (cd) is a TEM image of the catalyst prepared in Comparative Example 1 of the present invention after reacting at 580 degrees for 10 hours. As can be seen from the figure, the nano-alloy particles of the catalyst in Comparative Example 1 showed obvious sintering phenomenon during the reaction.

[0057] Figure 5 The figure shows the relationship between propane conversion rate and reaction duration in the carbon dioxide-assisted propane dehydrogenation experiment of Example 1 and Comparative Example 1 of the present invention. As can be seen from the figure, the catalyst deactivation rate of Example 1 of the present invention is extremely slow, indicating that the method of the present invention has a significant inhibitory effect on deactivation and can greatly improve the catalyst lifetime.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high thermally stable silica coated supported catalyst and a process for its preparation, characterized in that, The preparation method comprises the following steps: (1) loading active sites of a catalyst on the surface of a catalyst carrier and reducing the active sites into metal particles to obtain a supported catalyst; (2) mixing a solution of ethanol and concentrated ammonia water, denoted as solution A, and putting the supported catalyst into solution A to form a suspension; (3) mixing a solution of tetraethyl orthosilicate (TEOS) and ethanol, denoted as solution B, and continuously stirring solution B, and then injecting solution B into solution A at a certain speed; (4) stirring the mixed solution of solutions A and B for a certain time, collecting and washing the particles in the mixed solution; (5) drying the filtered solution after washing, calcining in an air environment, cooling the sample after calcination at room temperature, and finally obtaining the high-thermal-stability silica-coated supported catalyst.

2. The production method according to claim 1, characterized by, In step (1), the catalyst carrier can be an oxide carrier, a two-dimensional material carrier, a metal nanocluster or a molecular sieve, and the active site loading method can be an active site loading method such as impregnation, precipitation, sol-gel, hydrothermal synthesis, chemical bonding, mixing, ion exchange, melting, chemical vapor deposition, plasma flame, Joule heat loading, etc.

3. The preparation method according to claim 1, characterized in that, In step (1), the reduction method of the active sites can be a reduction method under a reducing atmosphere, plasma reduction, photochemical reduction, electrochemical reduction, biological reduction, liquid phase reduction, etc.

4. The method of claim 1, wherein, In step (2), the ratio of ethanol to concentrated ammonia water in solution A is 1:10 to 1:30, and the ammonia concentration of the concentrated ammonia water is 20%-30%.

5. The preparation method according to claim 1, characterized in that, The ratio of the mass of tetraethyl orthosilicate in the solution B to the total surface area of the supported catalyst in step (3) is 10-100 mg / m 2 The ratio of the volume of the ethanol solution to the volume of the solution A is 0.25-0.5, the stirring speed is 100-1000 r / min, and the injection speed of the solution is 10-100 μl / min.

6. The method of claim 1, wherein, In step (4), the stirring time is 0-12 hours after the injection is completed, the stirring speed is 100-1000 r / min, the collection method of the solution particles can be filtration, vacuum filtration, standing precipitation, centrifugation or high-temperature drying of the solution, and the washing solution can be deionized water or an ethanol solution.

7. The preparation method according to claim 1, characterized in that, In step (5), the drying temperature can be 40-120 degrees Celsius, the drying time can be 1-12 hours, the air environment calcination has a heating rate of 0.5-2°C / min, the calcination temperature is 300-500 degrees Celsius, and the calcination time is 1-12 hours.

8. A silica-coated supported catalyst with high thermal stability, characterized in that, The silica-coated supported catalyst is prepared by any one of the preparation methods of claims 1-7.

9. The high-thermo-stable silica-coated supported catalyst according to claim 8, characterized in that, The thickness of the silica coating is between 1-20 nm and can be adjusted as needed, the active sites are anchored by the silica coating, and the catalyst has strong metal-carrier interaction and sintering resistance.

10. The high-thermo-stable silica-coated supported catalyst according to claim 8, characterized in that, The catalyst surface contains a controllable number of silicon hydroxyl groups and free silicon elements, and part of the acid sites on the catalyst surface can be added according to the requirements, and the pore structure and coating density of the silica coating can be adjusted.

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