WO2024178847A1 - Photocatalyst for methane fluorination - Google Patents

Abstract

The present invention belongs to the field of catalysts, and particularly relates to a photocatalyst for methane fluorination. The catalyst is a titanium-based titanium peroxide complex particle material, and has catalytic activity towards methane under the illumination conditions of a wavelength of 390-450 nm, and a microscopic morphology shown as a spherical or near-spherical granular structure, with a villi-shaped nanostructure and/or a quantum dot nanostructure growing on the surface of the granular structure. The catalyst of the present invention can achieve an effective catalytic promotion effect for the perfluorination of methane, such that tetrafluoromethane can be directly and effectively prepared, the actual preparation difficulty, preparation energy consumption, etc. are reduced, and the utilization rate of materials and the methane fluorination efficiency can both be significantly improved.

Description

Photocatalysts for methane fluorination Technical Field

The invention belongs to the field of catalysts, and in particular relates to a photocatalyst for methane fluorination.

Background Art

Methane fluorination is generally a common and easy-to-implement process. Its fluorination products generally include monofluoromethane (CH ₃ F, methyl fluoride), difluoromethane (CH ₂ F ₂ , HFC-32), trifluoromethane (CHF ₃ , fluoroform) and tetrafluoromethane (CF ₄ , perfluoromethane), as well as other hybrid byproducts. Impurities such as fluorinated olefin compounds are easily present in different processes.

Therefore, although the fluorination process is easy to implement, there is currently no effective or efficient method to accurately obtain the target product.

Tetrafluoromethane, as an important product of methane fluorination, is widely used in the fields of plasma etching of integrated circuits, laser gases, low-temperature refrigerants, solvents, lubricants, insulating materials and coolants, and has a very wide range of use value. The existing tetrafluoromethane preparation process usually uses the intermediate methane fluoride chloride for preparation, such as the common preparation by mixing dichlorodifluoromethane or chlorotrifluoromethane with fluorine gas. There are also preparations by replacement reactions of carbon components and non-carbon components, such as the replacement fluorination of carbon monoxide or carbon dioxide or phosgene with sulfur tetrafluoride to prepare carbon tetrafluoride, and the preparation is directly prepared by reacting silicon carbide with fluorine gas as a raw material. However, the above preparation processes all have certain defects. The main problem is that the reaction conditions are relatively harsh, high temperature and high pressure mixed reaction is required, the efficiency is relatively low, and a large amount of raw material gas is required, among which fluorine gas has a large safety hazard in use, and its actual conversion rate is limited. Fluorine gas often requires a large excess, which makes tail gas treatment difficult. On the other hand, it can also be seen from the existing process that, as far as current technology is concerned, the perfluorination of methane is There is no mature and effective solution. The main reason is that the direct reaction of methane and fluorine will produce a large number of impurities mentioned above, with poor product selectivity, many types of impurities, difficult separation, low yield of target products, low material conversion utilization rate and other defects.

Therefore, at present, although patents such as US9404061 and US2407129 disclose technical solutions for preparing fluoromethane directly using methane as a raw material and have studied and improved the direct fluorination process of methane, most of them can only achieve the direct preparation of components such as trifluoromethane and trifluorochloromethane.

In this regard, improving and researching catalysts is an important direction. Catalysts have many unique properties that can promote the forward progress of the reaction or obtain the target product in a targeted manner. At present, most catalysts used for methane fluorination are halogen catalysts, such as chlorine. The halogenation of chlorine and the strong oxidizing property of fluorine can promote the forward progress of the reaction. However, as mentioned above, the current catalysts still cannot achieve the perfluorination of methane.

Summary of the invention

In order to solve the problems that the existing methane fluorination catalyst has limited use effect, cannot effectively and directly achieve the full fluorination of methane, and produces a large amount of impurities that need to be separated and removed, the present invention provides a photocatalyst for methane fluorination.

The main purposes of the present invention are: 1. to catalyze the perfluorination reaction of methane to prepare tetrafluoromethane; 2. to improve the effective utilization rate of raw materials in the methane fluorination process; 3. to improve the efficiency of methane fluorination and achieve high-efficiency fluorination. To achieve the above purposes, the present invention adopts the following technical solutions.

A photocatalyst for methane fluorination, the catalyst is a titanium-based titanium peroxide complex particle material, which has catalytic activity for methane under 390-450nm wavelength light conditions, and the microscopic morphology is a spherical or quasi-spherical particle structure, and the surface of the particle structure has a fuzzy nanostructure and/or a quantum dot nanostructure.

Preferably, the catalyst has catalytic activity for methane under the condition of 3.2-3.7 μmol/(m ₂ ·s) light quantum density. Preferably, the titanium-based titanium peroxide complex particles have titanium dioxide as the core, and the surface of the particles is covered with titanium peroxide. Complex.

Preferably, the preparation method of the catalyst comprises the following steps: 1) mixing a hydrated titanium dioxide block with an oxidant, stirring the mixture in an ice-water bath until the mixture is completely dissolved, and continuing to stir the mixture until the solid is completely dissolved to obtain a pre-liquid; 2) slowly adding titanium oxysulfate to the pre-liquid and continuously stirring the mixture until the solution is an orange-yellow clear solution or an orange-yellow transparent suspension, then removing water by rotary evaporation to obtain a concentrated suspension, placing the concentrated suspension in a water bath at 4 to 8° C. to grow crystals until the crystals precipitate and no longer increase, and separating and drying the crystals to obtain a catalyst.

Preferably, the oxidant in step 1) is hydrogen peroxide; and the molar ratio of the titanium dioxide contained in the hydrated titanium dioxide block in step 1) to the hydrogen peroxide contained in the hydrogen peroxide is 1:(2.5-3).

Preferably, the concentration of the hydrogen peroxide is 25-35wt%, the single addition amount of the hydrated titanium dioxide block is ≤12.5wt% of the total addition amount, and each time the hydrated titanium dioxide block is added, it is stirred until completely dissolved before continuing to be added. After all the hydrated titanium dioxide blocks are added to the hydrogen peroxide and completely dissolved, stirring is continued for 30-60 minutes.

It should be noted that the main purpose of controlling the amount of hydrated titanium dioxide blocks added in batches is to ensure the safety of the reaction and to avoid excessive reaction that may cause some components to separate out or cause safety hazards.

Preferably, the molar ratio of the titanyl sulfate used in step 2) to the titanium dioxide contained in the hydrated titanium dioxide block used in step 1) is (2-5):(95-98).

Preferably, in the rotary evaporation process of step 2), the original solution is concentrated to 25-40% of the original volume.

The present invention prepares a titanium dioxide catalytic material with high-efficiency photocatalytic performance through chemical synthesis. It is well known that titanium dioxide is a common photocatalyst with good photocatalytic activity. As a unique form of catalysis, photocatalysis can usually greatly accelerate the reaction process, reduce the reaction temperature, and thus achieve effective energy conservation and consumption reduction. In particular, for gas-gas reactions, photocatalysis is a very effective form of promotion.

However, there is no sufficient research and record on the photocatalytic fluorination of titanium dioxide. In this regard, the technical personnel of the present application have conducted a lot of research on the perfluorination process of methane catalyzed by catalysts.

It was found in the study that titanium dioxide, in combination with specific catalytic materials and specific fluorinating agents, can achieve catalytic fluorination of methane under specific conditions. However, its actual reaction efficiency is low, and the existing fluorination catalytic capacity can mostly only achieve the preparation of trifluoromethane or trifluorochloromethane. When combined with existing high-efficiency fluorination catalysts (such as chromium trioxide), it can only improve the efficiency of the catalytic reaction to form trifluoromethane or trifluorochloromethane, and the actual yield of tetrafluoromethane is less than 5%. The present invention improves the existing titanium dioxide catalyst, and uses an oxidant and titanium oxysulfate to form a titanium dioxide (TO)-titanium peroxide complex (PTC) composite preparation, and enhances the photocatalytic ability of titanium dioxide by compounding the titanium peroxide complex with titanium dioxide, and surface modification can form a nanostructure that is fuzzy and partially suspected of quantum dots (white bright part) as shown in Figure 1.

The photocatalytic performance of the catalyst after forming this structure is significantly enhanced and improved.

This is mainly because, after the formation of the titanium peroxide complex, the titanium dioxide-titanium peroxide complex (TO-PTC) has a large number of valence band holes (h ⁺ ), but due to the different hole potential energies of the two, they have different effects on methane.

However, due to the characteristics of the valence band holes themselves, they all have the following action process:
TiO ₂ +hv→TiO ₂ (e ^- +h ⁺ )
h ⁺ (TiO ₂ )+CH ₄ →CH ₄ ⁺ (I·)
h ⁺ (PTC)+CH ₄ →CH ₄ ⁺ (II·)

From the above, it can be seen that under the excitation of photoelectrons (hv), titanium dioxide can be excited to form valence band holes h ⁺ (TiO ₂ ), which can perform single-electron oxidation of methane to form a type of cationic radical state of methane CH ₄ ⁺ (I·), while the valence band holes h ⁺ (PTC) of the titanium peroxide complex can also perform single-electron oxidation of methane to form a type of cationic radical state of methane CH ₄ ⁺ (II·). The two types of cationic radical states of methane have different activities, or the two types of valence band holes have different actual effects on methane. For example, when methane is fluorinated by conventional processes under the action _of only titanium dioxide photoexcited valence band holes, it is easy to obtain more _CF2H2 and _CF3H compounds, and the total amount of the two can reach more than 85% of the total product, but the acquisition rate of _CF4 is low. When only the valence band holes h ⁺ (PTC) of the peroxide titanium complex are used, the actual products are less, the methane outflow rate reaches more than 80%, and the outflow rate of _CF4 is roughly between 9% and 12%. However, _{the CF2H2} and _CF3H compounds are The outflow rate of the product is only less than 2%, which shows that the valence band hole h ⁺ (PTC) of the actual peroxide titanium complex is more effective in exciting CF ₂ H ₂ and CF ₃ H compounds, and can form CF ₂ H ₂ ⁺ · and CF ₃ H ⁺ · cationic free radicals.

Therefore, the combination of the two can stimulate the raw materials and intermediate products in the perfluorination process of methane, thus providing the basis for perfluorination.

Then, the formed CF _a H _b ⁺ ·cation radical (a=0 or 1 or 2 or 3, b=1 or 2 or 3 or 4, and a+b=4) further undergoes a deprotonation reaction with water molecules or nitrogen molecules in the environment to form hydronium ions (H ₃ O ⁺ ) or protonated dinitrogen (N ₂ H ⁺ ). Taking hydronium ions (H ₃ O ⁺ ) as an example, it is shown as follows:
CF _a H _b ⁺ ·+H ₂ O→CF _a H _b-1 ·+H ₃ O ⁺

The CF _a H _b-1 · free radical formed after the reaction has extremely strong fluorination activity, and it can interact with electrophilic fluorinating agents such as common HF and F ₂ to achieve fluorination of the CF _a H _b-1 · free radical, as shown below:
CF _a H _b-1 ·+WF→CF _a+1 H _b-1 +W·

In the formula, W is composed of common electrophilic fluorinating agent elements such as H or F, that is, WF constitutes electrophilic fluorinating agents such as HF and F _2. The photoexcited electrons e ^- (TiO ₂ ) of titanium dioxide or the complex ions (N ^n- ) of the titanium peroxide complex interact with the hydrogen ions H ₃ O ⁺ generated in the second stage to form a complex, wherein the complex product of the complex ions depends on the actual components, such as in the technical solution of the present invention, forming water, and the photoexcited electrons e ^- (TiO ₂ ) interact with the hydrogen ions H ₃ O ⁺ to form hydrogen atoms H·, and the formed hydrogen atoms H· and W· further form a complex HW to complete the reaction cycle.

It can be seen that for the technical solution of the present invention, the combination of titanium dioxide and titanium peroxide complex is the key to achieve methane perfluorination. However, in additional experiments, it was found that the conversion rate of carbon tetrafluoride was reduced when _titanium dioxide was used as a photocatalyst to fluorinate methane to obtain the products _CF2H2 and _CF3H compounds, and then the products were catalyzed by titanium peroxide complex. This shows that the valence band holes of the titanium peroxide complex may still have an intermediate process of activation by photoexcited electrons ^e- ( _TiO2 ) and secondary excitation to form valence band holes, which also shows that the effective combination of titanium dioxide and titanium peroxide complex can achieve efficient and effective methane perfluorination.

In the catalyst preparation process, the pre-liquid obtained in step 1) can also be stirred continuously to obtain an orange-yellow solution, and The same post-treatment can also obtain the corresponding TO-PTC catalytic material, but the catalyst particles directly obtained by this method have poor uniformity of particle size, and the surface is relatively flat and smooth, with low specific surface area, and the catalytic efficiency and conversion rate are relatively limited. However, after adding titanyl sulfate, it can first form nucleation points to promote nucleation crystallization, that is, promote the TO-PTC catalyst grains to be effectively precipitated in a highly dispersed state, ensuring the uniformity of the grains, and due to the reducibility of titanyl sulfate and the oxidizability of the titanium peroxide complex, the two have a certain reaction, which promotes the growth of early grains and the growth coordination of the titanium peroxide complex and the titanium dioxide component, so that the titanium peroxide complex is not simply covered on the surface of the titanium dioxide particles, but forms a complex structure as shown in Figure 1, which is mainly composed of velvety nanostructures, and a small number of bright parts appear, similar to quantum dot structures. The addition of titanyl sulfate accelerates the preparation efficiency of the catalyst and increases its specific surface area, which has a significant effect on improving the catalytic efficiency, conversion selectivity and conversion rate of methane fluorination.

The beneficial effects of the present invention are as follows: the catalyst of the present invention can achieve a very effective catalytic promotion effect on the perfluorination of methane, can directly and effectively prepare tetrafluoromethane, and reduces the actual preparation difficulty, preparation energy consumption, etc., and the material utilization rate and methane fluorination efficiency can be significantly improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM characterization image of the catalyst product prepared in Example 1 of the present invention.

DETAILED DESCRIPTION

The present invention is further described in detail below in conjunction with specific embodiments and the accompanying drawings. A person of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

Unless otherwise specified, the hydrated titanium dioxide blocks used in the examples of the present invention are all commercially available products with a solid content (titanium dioxide content) of 9.2 wt %. Unless otherwise specified, the hydrogen peroxide used in the examples of the present invention are all commercially available with a concentration of 30 wt %.

Embodiment 1: A photocatalyst for methane fluorination, and its preparation method is as follows: 1) 82.5g of hydrated titanium dioxide block is mixed with 29mL of hydrogen peroxide, and the hydrated titanium dioxide block is added to the hydrogen peroxide in equal amounts in 10 times, and each addition is placed in an ice water bath and stirred to react until it is completely dissolved and then added, and after all the hydrated titanium dioxide blocks are added to the hydrogen peroxide, stirring is continued for 60 minutes after the solid is completely dissolved to obtain a pre-liquid; 2) 0.8g of titanium oxysulfate is slowly added to the pre-liquid and continuously stirred until the solution is an orange-yellow transparent solution, and water is removed by rotary evaporation to 30% of its original volume to obtain a concentrated suspension, and the concentrated suspension is placed in a 6°C water bath environment to grow grains until the grains are completely precipitated and no longer increase, and the grains are separated by centrifugation and dried at a constant temperature of 60°C to obtain a TO-PTC methane fluorination catalyst.

10g of the prepared catalyst was taken to carry out a conventional methane catalytic fluorination test. The methane catalytic test is as follows: the catalyst is filled into a transparent quartz reaction tube (a thin-diameter reaction tube is selected and the catalyst is basically in a full filling state), methane and fluorine nitrogen mixed gas are mixed as reaction gas and introduced into the reaction tube, and the time for the reaction gas to pass through the reaction tube is controlled to be at least 20s, that is, the flow rate is at most 3RV/min (RV is the reaction tube volume, which is the reaction tube volume). In this embodiment, the reaction gas flow rate is controlled to be 3RV/min, and the reaction temperature is controlled to be 360°C. During the reaction, a 390nm ultraviolet semiconductor laser light source is symmetrically arranged above and below the reaction tube, and the semiconductor laser light source is controlled to irradiate the reaction tube with a light quantum density of 3.5μmol/( _m2 ·s).

In the reaction gas, the molar ratio of methane to fluorine is controlled to be 1:2, and in the fluorine-nitrogen mixed gas, fluorine gas and nitrogen are mixed in a volume ratio of 1:9.

The reaction was carried out for a total of 15 minutes, and the fluorination catalytic reaction products were collected and characterized, and the effluent rate of each component (i.e., the proportion of the component in the effluent product) was calculated.

It can be seen from the test data in the above table that the catalyst of the present invention can be very effectively applied to the existing methane fluorination catalytic reaction, and can directly and efficiently realize the perfluorination catalysis of methane. Under the condition of a low contact time of 20s, the outflow rate of carbon tetrafluoride can reach 92.1%, and the impurity components _CF3H and _CF2H2 are _both converted in large quantities. It can be seen that the catalyst of the present invention has extremely strong catalytic selectivity and can efficiently realize the perfluorination catalysis of methane to obtain tetrafluoromethane.

In addition, the sample prepared in this embodiment was characterized, and the particle size characterization results showed that the particle size range was between 8.1 and 12.2 μm, with high particle size uniformity. At the same time, the catalyst sample was characterized by SEM, and the characterization results are shown in Figure 1. As can be seen from Figure 1, the catalyst prepared in this embodiment has a spherical or quasi-spherical morphology as a whole, and a fluff-like nanostructure grows on its surface, and combined with the TEM characterization results, it is shown that the fluff structure is PTC (titanium peroxide complex). And it can also be seen from Figure 1 that there is a bright white suspected quantum dot nanostructure on the surface of the spherical or quasi-spherical particle structure, and the component of this structure is titanium dioxide.

Example 2: A photocatalyst for methane fluorination, based on the preparation method of Example 1, only the amounts of hydrated titanium dioxide block, hydrogen peroxide and titanyl sulfate are adjusted, and some adjustments are made based on the molar amount calculated in the table below and then weighing the corresponding product amounts, and the molar amount is calculated based on the actual target raw material content (such as the titanium dioxide content in the hydrated titanium dioxide block and the hydrogen peroxide content in the hydrogen peroxide).

The above samples were subjected to the same characterization and testing as in Example 1.

The characterization results show that the SEM characterization results of sample 1-2-5 show that it presents a spherical or quasi-spherical shape, but when the amount of hydrogen peroxide is reduced, the villi-like structure of its microscopic morphology is significantly reduced or partially disappeared, and from the composition characterization results, the content of titanium peroxide complex is reduced. This is because after the amount of hydrogen peroxide is reduced, the amount of titanium peroxide complex formed is reduced, and during the preparation process, the solution is first formed into a suspension before it turns orange-yellow during the stirring process. There are very small amounts of particles that can be observed, and their existence is confirmed by optical analysis. This is also because the amount of hydrogen peroxide is too small, and the actual titanium dioxide is precipitated prematurely. This premature precipitation is not necessarily harmful. For this sample, the main problem is that the villi- _like structure cannot be effectively formed. In the subsequent performance characterization, the outflow rate of _CF4 dropped to 72.3%, the outflow rate of _CH4 further decreased to 0.9%, and the total outflow rate of _CF3H and _CF2H2 rose rapidly to 22.7%. It can be seen that the fuzzy structure formed by the titanium oxide complex has a significant promoting effect on the conversion of CF ₃ H and CF ₂ H ₂ , and is a key component and nanostructure that promotes the forward perfluorination of methane.

The 1-3.5-5 sample was characterized, and the characterization results showed that the particles were unstable particles, with a characterization morphology similar to that of flocculent precipitates, and in the performance test, the results were somewhat opposite to those of the 1-2-5 sample. In terms of outflow rate, the outflow rate of CH ₄ increased to 46.6%, the total outflow rate of CF ₃ H and CF ₂ H ₂ decreased to 3.3%, and the outflow rate of CF ₄ decreased to 39.2%, producing a large number of other impurities, such as fluoroethylene and other products, indicating that the titanium peroxide complex actually has a variety of activation effects on alkyl hydrogen atoms, and when the synergistic effect with titanium dioxide is not good, it is easy to cause the generation of impurities. The 1-3-0 sample is difficult to be effectively characterized, and most of it has a flocculent structure. When filling it for performance testing, it needs to be squeezed to a certain extent, indicating that it has volume expansion. The retest showed that the outflow rate of CH ₄ increased to 82.6%, the total outflow rate of CF ₃ H and CF ₂ H ₂ decreased to 1.2%, and the outflow rate of CF ₄ decreased to 10.1%.

In addition, the 1-2.5-2 sample was characterized, and its morphology and performance were close to those of Example 1, with a CH ₄ outflow rate of 1.6%, a total CF ₃ H and CF ₂ H ₂ outflow rate of 2.3%, and a CF ₄ outflow rate of 91.3%, indicating good selectivity and conversion rate.

Example 3: A photocatalyst for methane fluorination, based on the catalyst prepared in Example 1, only the catalytic conditions are adjusted during the catalytic fluorination process. Some of the adjustments are as follows to effectively illustrate the technical solution of the present invention.

The catalytic fluorination results of the above samples were recorded and compared, as shown in the following table.

Because the light excitation condition of titanium dioxide is determined based on the prior art, it needs to be irradiated with a wavelength of 390nm and above to effectively excite it to produce valence band holes. Therefore, the wavelength adjustment starts from 390nm. It can be seen from the above experiment that with the increase of light quantum density, the catalytic activity of titanium dioxide itself is enhanced, and on this basis, the catalytic efficiency of the titanium peroxide complex is insufficient, resulting in a decrease in the outflow rate of the target product. As the wavelength increases, there is no significant effect on the catalytic fluorination performance of titanium dioxide, but it can be seen from the 480-3.5 sample experimental group that the excessively high wavelength actually has a certain effect on the catalytic performance of the titanium peroxide complex. It can be seen that the actual titanium peroxide complex also has certain light-excited reaction conditions, and excessively high wavelengths will lead to unfavorable effects. Compared with other experimental groups, it can be seen that the conversion rate of _CF3H and _CF2H2 is significantly reduced, and in the case where the _methane outflow rate is basically not significantly changed, the content of other impurities is significantly increased, and it can be seen that side reactions have occurred. Therefore, for the catalyst of the present invention, although it has good catalytic selectivity and conversion rate, the catalytic conditions still need to be effectively controlled to ensure a good preparation effect.

Comparative Example 1: A combined catalyst for methane fluorination catalysis, comprising 10 g of titanium dioxide particles and 10 g of a titanium peroxide complex.

The titanium dioxide particles are commercially available 600 mesh titanium dioxide powder, which is filled into a transparent quartz reaction tube (I) as in Example 1 (a narrow diameter reaction tube is selected and the catalyst is basically in a state of filling). The titanium peroxide complex is based on the technical scheme of step 1) in Example 1. 86.8 g of hydrated titanium dioxide blocks and 102.1 mL of hydrogen peroxide are reacted to obtain a pre-liquid and then continue to stir until a clear orange-yellow solution is obtained. The flocculent titanium peroxide complex is then dried and precipitated to obtain a flocculent titanium peroxide complex, which is filled into a transparent quartz reaction tube (II) (a narrow diameter reaction tube is selected and the catalyst is basically in a state of filling). A mixture of methane and fluorine nitrogen is mixed as a reaction gas and introduced into the reaction tube, which passes through the reaction tube (I) and the reaction tube (II) in turn. The flow rate of the reaction gas in the reaction tube (I) and the reaction tube (II) is controlled to be 3RV/min, and the reaction temperature is controlled to be 360°C. During the reaction, a 390 nm ultraviolet semiconductor laser light source is symmetrically arranged above and below the reaction tube, and the semiconductor laser light source is controlled to be 3.5 μmol/(m ₂ The reaction tube is irradiated with a light quantum density of ·s).

That is, compared with Example 1, this comparative example is mainly to verify the synergistic coordination characteristics of titanium dioxide and titanium peroxide complex. In this comparative example, titanium dioxide and titanium peroxide complex are separated and each independently catalyzes methane and methane fluoride. The final experimental results are shown in the following table.

As can be seen from the table above, the effects of using the two independently are not excellent, and the catalytic selectivity for tetrafluoromethane has decreased significantly. This shows that the synergy between titanium dioxide and titanium peroxide complex is the key to producing good product selectivity, and it can be seen that when used alone, although the titanium peroxide complex has the ability to convert the intermediate methane fluoride, it has low activity and is not conducive to the perfluorination. In addition, a unique phenomenon was found from the test results, that is, the outflow rate of difluoromethane is higher than the outflow rate of trifluoromethane, indicating that the conversion rate of titanium peroxide complex for difluoromethane is low.

Compared with Example 1, this comparative example actually prolongs the contact reaction time of the reaction gas, but the reaction effect is far less than that of Example 1. It can also be seen that the coordination of the two main components of the catalyst of the present invention, titanium dioxide and titanium peroxide complex, is very critical.

In summary of the above, it is also necessary to explain and note that: through experiments, the catalyst of the present invention has been confirmed and verified to be effective for the perfluorination of methane, and it is also possible that it has a promoting effect on the perfluorination and/or partial fluorination of other alkane compounds. The optimal fluorination process is not yet known, but the protection scope of the catalyst of the present invention should not only be limited to the application in the field of methane catalysis, but the catalyst of the present invention should be regarded as a core entity.

Claims (8)

A photocatalyst for methane fluorination, characterized in that: The catalyst is a titanium-based titanium peroxide complex particle material, which has catalytic activity for methane under 390-450nm wavelength light conditions, and has a microscopic morphology of a spherical or quasi-spherical particle structure, with a fluffy nanostructure and/or a quantum dot nanostructure growing on the surface of the particle structure. The photocatalyst for methane fluorination according to claim 1, characterized in that The catalyst has catalytic activity for methane under the condition of light quantum density of 3.2-3.7 μmol/(m ₂ ·s). The photocatalyst for methane fluorination according to claim 1, characterized in that The titanium-based titanium peroxide complex particles have titanium dioxide as the core, and the surface of the particles is covered with a titanium peroxide complex. A photocatalyst for methane fluorination according to claim 1, 2 or 3, characterized in that: The preparation method of the catalyst comprises the following steps: 1) Mixing the hydrated titanium dioxide block with the oxidant, stirring in an ice water bath until completely dissolved, and continuing to stir until the solid is completely dissolved to obtain a pre-liquid; 2) Slowly add titanyl sulfate to the preliquid and continue stirring until the solution becomes an orange-yellow clear solution or an orange-yellow transparent suspension, remove water by rotary evaporation to obtain a concentrated suspension, place the concentrated suspension in a 4-8°C water bath environment to grow crystals until crystals precipitate and no longer increase, separate and dry the crystals to obtain the catalyst. The photocatalyst for methane fluorination according to claim 4, characterized in that Step 1) The oxidant is hydrogen peroxide; In step 1), the molar ratio of titanium dioxide contained in the hydrated titanium dioxide block to hydrogen peroxide contained in the hydrogen peroxide is 1 (2.5-3). The photocatalyst for methane fluorination according to claim 5, characterized in that The concentration of the hydrogen peroxide is 25-35wt%, the single addition amount of the hydrated titanium dioxide block is ≤12.5wt% of the total addition amount, and each time the hydrated titanium dioxide block is added, it is stirred until it is completely dissolved before continuing to be added. After all the hydrated titanium dioxide blocks are added to the hydrogen peroxide and completely dissolved, stirring is continued for 30-60 minutes. The photocatalyst for methane fluorination according to claim 4, characterized in that The molar ratio of the titanyl sulfate used in step 2) to the titanium dioxide contained in the hydrated titanium dioxide block used in step 1) is (2-5): (95-98). The photocatalyst for methane fluorination according to claim 4, characterized in that In step 2), the rotary evaporation process is used to concentrate the original solution to 25-40% of the original volume.