A catalyst for photo-thermal catalytic conversion of methane to formaldehyde under gas-solid continuous flow and a preparation method and application thereof

Abstract

The application relates to the field of new energy chemical catalysis, in particular to a catalyst for photo-thermal catalysis of methane to formaldehyde under gas-solid continuous flow and a preparation method and application thereof. The preparation method comprises the following steps: S1, pretreatment carrier preparation; S2, precursor solution preparation: S201, adding a palladium chloride solution to a zinc oxide suspension, stirring at room temperature, vacuum suction filtration, washing and drying to obtain a Pd / ZnO precursor; S202, dispersing the Pd / ZnO precursor in deionized water, adding a rare earth metal salt, then adding triethylenetetramine dropwise, stirring, and then adding sodium hypophosphite to obtain a precursor solution; S3, composite precursor preparation; S4, post-treatment. The application provides a catalyst for photo-thermal catalysis of methane to formaldehyde under gas-solid continuous flow and a preparation method and application thereof, so as to solve the problems of great difficulty in methane C-H bond activation, easy deep oxidation of formaldehyde and low operation efficiency of the catalyst in a gas-solid continuous flow system in the related art.

Description

Technical Field

[0001] This application relates to the field of new energy chemical catalysis technology, and in particular to a catalyst for the photothermal catalysis of methane to formaldehyde under continuous gas-solid flow, its preparation method and application. Background Technology

[0002] Formaldehyde is a basic chemical raw material used in the synthesis of phenolic resins, formalin, and other products, holding an irreplaceable position in many industrial fields. Currently, the main industrial method for producing formaldehyde is methanol oxidation. There are two main methanol oxidation methods: silver catalysis and iron-molybdenum catalysis. Silver catalysis is a more traditional but still widely used method, typically converting methanol to formaldehyde at high temperatures of 600–720 °C. This method has a short catalyst life, a high methanol content in the product, and a high reaction temperature. Iron-molybdenum oxidation is a more modern and efficient method, dominating in large and newly built plants. It reacts methanol with oxygen to produce formaldehyde and water at temperatures of 250–400 °C. This catalyst is expensive and prone to poisoning, and requires high purity raw materials. More importantly, the industrial production of methanol is complex and energy-intensive. Industrially, methane is typically first converted to syngas (CO and H2) at high temperatures of 800–1000 °C, and then the syngas is converted to methanol via Fischer-Tropsch synthesis. It is evident that the current industrial production of formaldehyde involves extremely complex steps, high energy consumption, and significant carbon emissions.

[0003] However, the carbon-hydrogen bond (CH) of CH4 is very stable (bond energy as high as 439 KJ / mol), requiring high energy to break, making direct conversion difficult. Photothermal catalysis can overcome thermodynamic limitations, using light to lower the reaction energy barrier and heat to improve catalytic efficiency. However, formaldehyde's activation energy is lower than methane's, so methane is usually peroxidized to CO2. Currently, the main approach is to design catalysts to improve methane conversion efficiency and formaldehyde selectivity, but catalysts developed in recent years are mainly suitable for methane conversion in closed systems. However, in closed reactors, the product and catalyst cannot be separated in time, leading to product peroxidation on the catalyst surface and preventing continuous accumulation, which does not meet industrial requirements. Flow reactors can separate products in time, enabling real-time collection of formaldehyde and continuous methane conversion. However, current research on the direct photothermal catalytic conversion of methane to formaldehyde in flow systems is limited, and the catalytic efficiency is very low. Therefore, developing efficient catalysts for flow systems is crucial for reforming formaldehyde production. Summary of the Invention

[0004] This application provides a catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow, its preparation method, and its application, in order to solve the problems of high difficulty in activating the CH bond of methane, easy deep oxidation of formaldehyde, and low operating efficiency of catalysts in continuous gas-solid flow systems in related technologies.

[0005] In a first aspect, a method for preparing a catalyst for the photothermal catalytic production of formaldehyde from methane in a continuous gas-solid flow is provided, comprising the following steps: S1. Preparation of pretreated carrier: The composite carrier was dispersed in deionized water, ultrasonically dispersed for 15-20 min, and then dried at 105-110℃ to obtain the pretreated carrier. S2. Preparation of precursor solution: S201. Disperse ZnO in deionized water at a mass ratio of 1:5 to obtain a zinc oxide suspension; A palladium chloride solution was added to a zinc oxide suspension, stirred at room temperature for 1–2 h, vacuum filtered, washed, and dried to obtain a Pd / ZnO precursor; the Pd loading was 2–3 wt% relative to the ZnO mass. S202. Disperse the Pd / ZnO precursor in deionized water and sonicate for 15-20 min to form a Pd / ZnO dispersion. Weigh rare earth metal salts according to the Pd:X molar ratio of 1:(0.4-0.5) and add them to the Pd / ZnO dispersion. Stir for 20-25 min. Add triethylenetetramine dropwise to adjust the pH to 7.5-8, stir, add sodium hypophosphite, and continue stirring for 30-40 minutes to obtain the precursor solution; X is selected from Ce and La, and the mass ratio of sodium hypophosphite to Pd / ZnO precursor is 1:(1.5~2). S3. Preparation of composite precursor: The pretreated carrier was added to the precursor solution, vacuum impregnated for 3-4 hours, and dried to obtain the loaded precursor. The loaded precursor was placed in a tube furnace, H2 was introduced, and the temperature was raised to 400~450℃ at room temperature and held for 4.5~7h to obtain the composite precursor. S4. Post-processing: The composite precursor was immersed in the modified liquid, stirred at room temperature for 1 hour, ultrasonically dispersed for 10-15 minutes, filtered, dried at 75-80℃ for 4-6 hours, and then calcined at 350-360℃ for 0.5-1 hour under nitrogen protection to obtain a gas-solid continuous flow photothermal catalytic catalyst for the production of formaldehyde from methane. The modified solution comprises catechol resin, γ-aminopropyltriethoxysilane, acetylacetone, and ethanol solution in a mass ratio of 2:1:(0.5~0.7):20.

[0006] Preferably, the composite carrier comprises a photothermal carrier and a structural reinforcement carrier in a mass ratio of 1:(1~2); The method for preparing the photothermal carrier includes the following steps: Biochar and boron mud were mixed in a mass ratio of 3:2, impregnated in a 5wt% hydrochloric acid solution for 25-30 minutes, washed until neutral, and dried at 105-110℃ to obtain a composite matrix. The composite matrix is ​​mixed with nickel phosphide and ground in a ball mill for 1.5-2 hours to obtain a photothermal carrier; The mass ratio of the boron mud to nickel phosphide is 1:(0.2~0.5); The method for preparing the structural reinforcement carrier includes the following steps: Diatomaceous earth and perlite were mixed at a mass ratio of 4:(2~3) and dried at 110~120℃ for 3~4 hours. The mixture was then dispersed in a sodium gellan gum aqueous solution at 80℃, stirred for 1 hour, and dried at 100~105℃ for 2~3 hours to obtain a structural reinforcement carrier.

[0007] Preferably, the concentration of the sodium gellan gum aqueous solution is 8-10 wt%.

[0008] Preferably, the method for preparing the biochar includes the following steps: After crushing the straw to 0.5~2mm, it is placed in a closed carbonization furnace and heated to 500~550℃ at a rate of 10℃ / min under nitrogen protection. The carbonization is carried out at a constant temperature for 2~3 hours and then cooled to room temperature to obtain biochar.

[0009] Preferably, in S202, the rare earth metal salt is selected from either cerium nitrate or lanthanum nitrate.

[0010] Preferably, step S3, heating to 400-450°C at room temperature and holding at that temperature for 4.5-7 hours, includes the following steps: The temperature was raised from room temperature to 260℃ and held for 1.5~2 hours at a rate of 2℃ / min. The temperature is increased from 260℃ to 400~450℃ and held for 3~5 hours, with a heating rate of 5℃ / min.

[0011] Preferably, in step S3, the H2 flow rate is 80 mL / min.

[0012] Preferably, in the ethanol solution of the modified liquid, the mass ratio of anhydrous ethanol to deionized water is 3:1.

[0013] Secondly, a catalyst for the photothermal catalytic production of formaldehyde from methane via a continuous gas-solid flow is provided, which is prepared by any of the above-described methods for preparing the catalyst for the photothermal catalytic production of formaldehyde from methane via a continuous gas-solid flow.

[0014] Thirdly, the catalyst described above for the photothermal catalytic conversion of methane to formaldehyde under continuous gas-solid flow is provided for its application in the direct conversion of methane to formaldehyde under continuous gas-solid flow photothermal catalytic flow.

[0015] The beneficial effects of the technical solution provided in this application include: This application provides a photothermal catalytic catalyst for the production of formaldehyde from methane under a continuous gas-solid flow, its preparation method, and its application. The catalyst employs an impregnation-hydrogen calcination method, in which Pd is supported on a semiconductor ZnO. Under the action of hydrogen and Pd, ZnO… 2+ The metal is reduced to metallic Zn and precipitates from the crystal lattice, simultaneously forming a PdZn alloy with Pd in ​​situ, yielding Pd / ZnO material. Further, Ce / La metal doping is then applied to Zn... 2+ Before being reduced, TETA acts as a complexing agent with Ce. 3+ / La 3+ Stable complexes are formed, and their uniform dispersion on the Pd / ZnO surface is promoted. During the alloying process, the PdZn alloy and the ZnO support form a strong metal-support interaction to obtain PdZn / ZnO. Ce / La doping regulates the d-band center of Pd and enhances the activation ability of methane CH bonds. The introduction of Pd changes the state of lattice oxygen in ZnO and promotes the cycling of lattice oxygen. The PdZn formed therein acts as the "heart" of the entire cycle. On the one hand, it pumps highly active interfacial lattice oxygen for the oxidation of methane. On the other hand, it strongly pumps hydroxyl groups from water to fill vacancies, thereby achieving a highly efficient and stable catalytic cycle.

[0016] The photothermal carrier utilizes the narrow bandgap of Ni2P to efficiently absorb light energy, increasing the surface temperature of the catalyst and providing sufficient photothermal energy for methane activation. The hierarchical porous structure constructed by the structural reinforcement carrier reduces the gas mass transfer resistance of the continuous flow system, preventing product accumulation on the catalyst surface and adapting to continuous flow bed operation. At the same time, it enhances the mechanical strength and stability of the catalyst. In the modifier, γ-aminopropyltriethoxysilane (KH550) serves as an inorganic crosslinking component, crosslinking catechol resin with carriers such as ZnO and diatomaceous earth. The catechol resin contains a large number of ortho-phenolic hydroxyl groups, which simultaneously form hydrogen bonds with the hydroxyl groups on the ZnO surface, playing a spatial confinement role, shortening the formaldehyde adsorption residence time, and inhibiting deep oxidation. Acetylacetone acts as a chelating stabilizer to complex free metal ions and inhibit grain agglomeration. The prepared catalyst can achieve continuous catalytic methane conversion (conversion of methane to the high-value chemical formaldehyde) under solar energy drive at low temperature conditions (100℃), and continuously produce formaldehyde, meeting the needs of industrial production. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the preparation method of the catalyst for the photothermal catalytic production of formaldehyde from methane in a continuous gas-solid flow process provided in this application. Figure 2 The in-situ EPR spectra of the catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow, prepared in Example 1 of this application, and ZnO. Figure 3 A schematic diagram showing the product yield of the catalysts for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow provided in this application, as prepared in Comparative Example 1 and Example 1. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] See Figures 1-3 As shown, this application provides a catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow, its preparation method, and its application.

[0021] Example 1 The preparation method of the catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow provided in this embodiment includes the following steps: S1. Preparation of pretreated carrier: 15g of composite carrier was dispersed in 50mL of deionized water, ultrasonically dispersed for 15min, dried, and dried at 110℃ to obtain the pretreated carrier. S2. Preparation of precursor solution: S201. Disperse 20g of commercial zinc oxide (ZnO) in 100g of deionized water and sonicate for 20min to obtain a zinc oxide suspension; 0.67 g of palladium chloride was dissolved in 50 mL of deionized water. After complete dissolution, a palladium chloride solution was obtained. The palladium chloride solution was added to a zinc oxide suspension and stirred at room temperature for 1.5 h. After vacuum filtration, washing and drying, the Pd / ZnO precursor was obtained. The Pd loading is 2 wt% relative to the ZnO mass. S202. Disperse 15g of Pd / ZnO precursor in 80mL of deionized water and sonicate for 15min to form a Pd / ZnO dispersion. Weigh 0.49g of cerium nitrate [Ce(NO3)3·6H2O] and add it to the Pd / ZnO dispersion. Stir for 25min. Add 2 mL of triethylenetetramine to adjust the pH to 7.7, stir, add 7.5 g of sodium hypophosphite, and continue stirring for 30 min to obtain the precursor solution; S3. Preparation of composite precursor: The pretreated carrier was added to the precursor solution, vacuum impregnated for 3 hours, and dried to obtain the loaded precursor. The loaded precursor was placed in a tube furnace, and H2 was introduced (flow rate of 80 mL / min). The temperature was raised from room temperature to 260 °C and held for 1.5 h at a rate of 2 °C / min. Then the temperature was raised from 260 °C to 400 °C and held for 4 h at a rate of 5 °C / min. After cooling to room temperature, the composite precursor was obtained. S4. Post-processing: The composite precursor was immersed in the modification liquid, stirred at room temperature for 1 hour, ultrasonically dispersed for 10 minutes, filtered, dried at 75°C for 6 hours, and then calcined at 360°C under a nitrogen atmosphere for 1 hour to obtain a catalyst for the photothermal catalytic production of formaldehyde from methane in a continuous gas-solid flow.

[0022] Among them, the composite carrier in S1 includes a photothermal carrier and a structural reinforcement carrier with a mass ratio of 1:1.5; The method for preparing a photothermal carrier includes the following steps: 10g of biochar and 6.7g of boron mud were mixed evenly, impregnated with 5wt% hydrochloric acid solution for 30min, washed until neutral, and dried at 110℃ for 2h to obtain the composite matrix. The composite matrix was mixed with 2.68g of nickel phosphide and ground in a ball mill for 1.5h to obtain the photothermal carrier.

[0023] The method for preparing biochar is as follows: After crushing the straw to 0.5~2mm, it is placed in a closed carbonization furnace and heated to 500℃ at a rate of 10℃ / min under nitrogen protection. The carbonization is carried out at a constant temperature for 3 hours and then cooled to room temperature to obtain biochar.

[0024] The method for preparing a structurally reinforced carrier includes the following steps: 20g of diatomaceous earth and 15g of perlite were mixed and dried at 110℃ for 4h. The mixture was then dispersed in a 10wt% sodium gellanate aqueous solution at 80℃, stirred for 1h, and dried at 100℃ for 3h to obtain a structurally reinforcing carrier.

[0025] In step S4, the modified solution is a mixture of 10g catechol resin (catechol type thermosetting phenolic resin, Resol type, number average molecular weight 1000 Da, solid content 50wt%, solvent is ethanol solution, the same below), 5g γ-aminopropyltriethoxysilane, 3g acetylacetone and 100g ethanol solution, wherein the mass ratio of anhydrous ethanol to water in the ethanol solution is 3:1.

[0026] Example 2 The difference between this embodiment and Embodiment 1 is that the composite carrier in S1 includes a photothermal carrier and a structural reinforcement carrier in a mass ratio of 1:1; and in step S4, the modified liquid is a mixture of 10g catechol resin, 5g γ-aminopropyltriethoxysilane and 100g ethanol solution, while the rest is the same as in Embodiment 1.

[0027] Example 3 The preparation method of the catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow provided in this embodiment includes the following steps: S1. Preparation of pretreated carrier: 15g of composite carrier was dispersed in 50mL of deionized water, ultrasonically dispersed for 20min, dried, and dried at 105℃ to obtain the pretreated carrier. S2. Preparation of precursor solution: S201. Disperse 20g of commercial zinc oxide (ZnO) in 100g of deionized water and sonicate for 20min to obtain a zinc oxide suspension; 1 g of palladium chloride was dissolved in 50 mL of deionized water. After complete dissolution, a palladium chloride solution was obtained. The palladium chloride solution was added to a zinc oxide suspension and stirred at room temperature for 1 h. After vacuum filtration, washing and drying, the Pd / ZnO precursor was obtained. The Pd loading is 3 wt% relative to the ZnO mass. S202. Disperse 15g of Pd / ZnO precursor in 80mL of deionized water and sonicate for 20min to form a Pd / ZnO dispersion. Weigh 0.92g of cerium nitrate [Ce(NO3)3·6H2O] and add it to the Pd / ZnO dispersion. Stir for 25min. Add 1.8 mL of triethylenetetramine to adjust the pH to 7.5, stir, add 10 g of sodium hypophosphite, and continue stirring for 30 min to obtain the precursor solution; S3. Preparation of composite precursor: The pretreated carrier was added to the precursor solution, vacuum impregnated for 4 hours, and dried to obtain the loaded precursor. The loaded precursor was placed in a tube furnace, and H2 was introduced (flow rate of 80 mL / min). The temperature was raised from room temperature to 260 °C and held for 2 h at a rate of 2 °C / min. Then the temperature was raised from 260 °C to 450 °C and held for 3 h at a rate of 5 °C / min. After cooling to room temperature, the composite precursor was obtained. S4. Post-processing: The composite precursor was immersed in the modification liquid, stirred at room temperature for 1 hour, ultrasonically dispersed for 15 minutes, filtered, dried at 80°C for 4 hours, and then calcined at 350°C under a nitrogen atmosphere for 1 hour to obtain a gas-solid continuous flow photothermal catalyst for the production of formaldehyde from methane.

[0028] Among them, the composite carrier in S1 includes a photothermal carrier and a structural reinforcement carrier with a mass ratio of 1:2; The method for preparing a photothermal carrier includes the following steps: 10g of biochar and 6.7g of boron mud were mixed evenly, impregnated with 5wt% hydrochloric acid solution for 25min, washed until neutral, and dried at 105℃ for 2h to obtain the composite matrix. The composite matrix was mixed with 1.34g of nickel phosphide and ground in a ball mill for 2 hours to obtain the photothermal carrier.

[0029] The method for preparing biochar is as follows: After crushing the straw to 0.5~2mm, it is placed in a closed carbonization furnace and heated to 550℃ at a rate of 10℃ / min under nitrogen protection. The carbonization is carried out at a constant temperature for 2 hours and then cooled to room temperature to obtain biochar.

[0030] The method for preparing a structurally reinforced carrier includes the following steps: 20g of diatomaceous earth and 10g of perlite were mixed and dried at 120℃ for 3h. The mixture was then dispersed in an 8wt% sodium gellanate aqueous solution at 80℃, stirred for 1h, and dried at 105℃ for 2h to obtain a structurally reinforcing carrier.

[0031] In step S4, the modified solution is a mixture of 10g catechol resin, 5g γ-aminopropyltriethoxysilane, 3.5g acetylacetone and 100g ethanol solution, wherein the mass ratio of anhydrous ethanol to water in the ethanol solution is 3:1.

[0032] Example 4 The preparation method of the catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow provided in this embodiment includes the following steps: S1. Preparation of pretreated carrier: 15g of composite carrier was dispersed in 50mL of deionized water, ultrasonically dispersed for 20min, dried, and dried at 110℃ to obtain the pretreated carrier. S2. Preparation of precursor solution: S201. Disperse 20g of commercial zinc oxide (ZnO) in 100g of deionized water and sonicate for 20min to obtain a zinc oxide suspension; 1 g of palladium chloride was dissolved in 50 mL of deionized water. After complete dissolution, a palladium chloride solution was obtained. The palladium chloride solution was added to a zinc oxide suspension and stirred at room temperature for 1.5 h. After vacuum filtration, washing and drying, the Pd / ZnO precursor was obtained. The Pd loading is 3 wt% relative to the ZnO mass. S202. Disperse 15g of Pd / ZnO precursor in 80mL of deionized water and sonicate for 15min to form a Pd / ZnO dispersion. Weigh 0.8g of lanthanum nitrate [La(NO3)3·6H2O] and add it to the Pd / ZnO dispersion. Stir for 25min. Add 2.1 mL of triethylenetetramine to adjust the pH to 8, stir, add 7.5 g of sodium hypophosphite, and continue stirring for 30 min to obtain the precursor solution; S3. Preparation of composite precursor: The pretreated carrier was added to the precursor solution, vacuum impregnated for 4 hours, and dried to obtain the loaded precursor. The loaded precursor was placed in a tube furnace and H2 was introduced (flow rate of 80 mL / min). The temperature was raised from room temperature to 260 °C and held for 2 h at a rate of 2 °C / min. Then the temperature was raised from 260 °C to 420 °C and held for 5 h at a rate of 5 °C / min. After cooling to room temperature, the composite precursor was obtained. S4. Post-processing: The composite precursor was immersed in the modification liquid, stirred at room temperature for 1 hour, ultrasonically dispersed for 10 minutes, filtered, dried at 75°C under a nitrogen atmosphere for 5 hours, and then calcined at 360°C for 0.5 hours to obtain a catalyst for the photothermal catalytic production of formaldehyde from methane in a continuous gas-solid flow.

[0033] Among them, the composite carrier in S1 includes a photothermal carrier and a structural reinforcement carrier with a mass ratio of 1:1.5; The method for preparing a photothermal carrier includes the following steps: Mix 10g of biochar with 6.7g of boron mud evenly, impregnate with 5wt% hydrochloric acid solution for 30min, wash until neutral, and dry at 100℃ for 2h to obtain composite matrix; The composite matrix was mixed with 3.35g of nickel phosphide and ground in a ball mill for 2 hours to obtain the photothermal carrier.

[0034] The method for preparing biochar is as follows: After crushing the straw to 0.5~2mm, it is placed in a closed carbonization furnace and heated to 520℃ at a rate of 10℃ / min under nitrogen protection. The carbonization is carried out at a constant temperature for 2 hours and then cooled to room temperature to obtain biochar.

[0035] The method for preparing a structurally reinforced carrier includes the following steps: 20g of diatomaceous earth and 12g of perlite were mixed and dried at 110℃ for 4h. The mixture was then dispersed in a 10wt% sodium gellanate aqueous solution at 80℃, stirred for 1h, and dried at 105℃ for 3h to obtain a structurally reinforcing carrier.

[0036] In step S4, the modified solution is a mixture of 10g catechol resin, 5g γ-aminopropyltriethoxysilane, 2.5g acetylacetone and 100g ethanol solution, wherein the mass ratio of anhydrous ethanol to water in the ethanol solution is 3:1.

[0037] Example 5 The difference between this embodiment and embodiment 4 is that S202 includes the following steps: S202. Disperse 15g of Pd / ZnO precursor in 80mL of deionized water and sonicate for 15min to form a Pd / ZnO dispersion. Weigh 0.64g of lanthanum nitrate [La(NO3)3·6H2O] and add it to the Pd / ZnO dispersion. Stir for 25min. Add 2.1 mL of triethylenetetramine to adjust the pH to 8, stir, add 7.5 g of sodium hypophosphite, and continue stirring for 30 min to obtain the precursor solution.

[0038] Comparative Example 1 The difference from Example 1 is that in this comparative example, the pretreatment carrier is replaced with an equal amount of structurally reinforcing carrier, and sodium hypophosphite is not added in step S202.

[0039] Comparative Example 2 The difference from Example 1 is that sodium hypophosphite is not added in step S202 in this comparative example, and the impregnation of the modified solution is not performed in step S4.

[0040] Comparative Example 3 The difference from Example 1 is that, in this comparative example, the pretreatment carrier is replaced with an equal amount of structural reinforcement carrier, and the structural reinforcement carrier in this comparative example is diatomaceous earth and perlite in a mass ratio of 1:1 (dried at 110°C for 4 hours after mixing); no cerium nitrate loading is performed in S202, that is, no cerium nitrate [Ce(NO3)3·6H2O] is added.

[0041] Comparative Example 4 The difference from Example 1 is that in this comparative example, cerium nitrate is not loaded in S202, that is, cerium nitrate [Ce(NO3)3·6H2O] is not added, and the impregnation of the modified liquid is not performed in step S4.

[0042] It should be noted that, in the above embodiments and comparative examples, step S3 was carried out in an H2 atmosphere. H2 is a stronger reducing agent than the decomposition products of sodium hypophosphite, and thermodynamics and kinetics tend to reduce Pd... 2+ Restore to Pd 0 The newborn Pd 0 Nanoparticles, acting as active sites for hydrogen dissociation and overflow, can significantly promote the partial reduction of the surrounding ZnO surface, thereby generating Zn from the ZnO surface. 0 This leads to the formation of PdZn alloys. The continuous flow of H2 will carry away the gaseous products of the reaction, inhibiting excessively high local phosphorus species concentrations and thus suppressing the deep formation of phosphides.

[0043] The catalysts for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow obtained by the above-described embodiments and comparative examples (hereinafter referred to as catalysts) were tested.

[0044] Methane activation capacity and formaldehyde selectivity test: 50 mg of catalyst was loaded into a quartz reaction tube, and the feed gas was introduced. After purging for 30 minutes under dark conditions, the xenon lamp (simulating sunlight, light intensity 600 mW / cm²) was turned on. 2 When the temperature stabilized at 110±5℃, it was recorded as the reaction start time. After the reaction had been running stably for 1 hour, sampling began. The product components were analyzed using a gas chromatograph (GC-2014, equipped with an FID detector and a Porapak Q column) to quantify the concentrations of methane (CH4), formaldehyde (HCHO), and carbon dioxide (CO2). Samples were then collected every 1 hour for a total of 5 times, and the average value was taken as the final result.

[0045] The feed gas is CH4:water vapor = 1:9 (volume ratio), with a space velocity of 2000 h⁻¹. -1 .

[0046] The methane conversion rate is calculated as follows: The methanol selectivity is calculated as follows: The formula for calculating formaldehyde peroxidation rate is: See Table 1 for details.

[0047] Table 1 In the formation of the PdZn alloy, Pd is first loaded onto ZnO via impregnation, and then calcined under a hydrogen atmosphere. H2, acting as a reducing agent, reacts with ZnO, causing some of the Zn to be deposited. 2+The Zn alloy is reduced to metallic Zn and precipitates from the crystal lattice, simultaneously forming a PdZn alloy in situ with Pd. The Zn precipitation directly leaves oxygen vacancies (Vo) in the ZnO crystal lattice. The formation of these oxygen vacancies disrupts the periodic structure of the ZnO lattice, making the surrounding lattice oxygen atoms unstable and more reactive, more likely to attack the CH bonds of methane, thus promoting methane activation. Pd, especially PdZn alloys, are excellent H2O dissociation catalysts. They can easily break the H2O bonds, activating H2O into highly reactive hydroxyl groups. The hydroxyl groups generated on the surface of the PdZn alloy can rapidly migrate to the oxygen vacancies on the adjacent ZnO support, completing the regeneration of lattice oxygen. In the catalyst provided in this application, lattice oxygen is no longer a static lattice component, but a dynamic support that rapidly cycles between "oxygen vacancies" and "active oxygen." As the "heart" of the entire cycle, the PdZn alloy pumps highly active interfacial lattice oxygen for methane oxidation on the one hand, and powerfully pumps hydroxyl groups from water to fill vacancies on the other, thus achieving a highly efficient and stable catalytic cycle.

[0048] See Figure 2 As shown, this is the in-situ EPR spectrum of the catalyst of Example 1 and ZnO. Four peaks can be seen, with the ratio of peaks from left to right being 1:2:2:1. This is a very obvious characteristic signal of hydroxyl radicals. Compared with pure ZnO, the catalyst prepared in Example 1 has a higher signal intensity of hydroxyl radicals, proving that the loading of Pd and Ce accelerates the activation of H2O to highly reactive hydroxyl groups.

[0049] In the examples, the photothermal carrier has high photothermal conversion efficiency, providing sufficient energy for the activation of methane CH bonds. The doping of lanthanum nitrate / cerium nitrate regulates the d-band center of the PdZn alloy, enhancing the methane adsorption and activation ability, and the conversion rate is slightly higher than that of the comparative example. The modified solution uses a high-molecular-weight polyphenol resin (catechol resin), where the phenolic hydroxyl groups (-OH) form stable hydrogen bonds with the hydroxyl groups on the ZnO surface, shortening the formaldehyde adsorption residence time. γ-aminopropyltriethoxysilane (KH-550) plays a cross-linking role, and acetylacetone acts as a chelating stabilizer, complexing the free metal ions at the Pd and Zn active sites on the catalyst surface, inhibiting the sintering and growth of active component grains at high temperatures, resulting in a fast formaldehyde desorption rate and a significant reduction in peroxidation rate. In Example 2, compared to Example 1, acetylacetone was not used in the modified solution, and metal ions migrated and agglomerated, resulting in slower formaldehyde desorption and an increased peroxidation rate.

[0050] Examples 4 and 5 use La doping, which has a slightly better electronic modulation effect than Ce, so the methane conversion rate is slightly higher than that of Example 1. In Example 3, the reduced Ni2P ratio and excessive Pd loading led to the aggregation of active sites, resulting in a slightly lower conversion rate.

[0051] In the comparative examples, the lack of a photothermal carrier in Comparative Examples 1 and 3 resulted in insufficient photothermal energy, unoptimized alloy electronic structure, increased methane activation energy barrier, and decreased conversion rate. Comparative Examples 2 and 4 lacked impregnation with the modified liquid, and the catalyst surface had no modification layer, making formaldehyde easily peroxidized to CO2, while the formaldehyde selectivity decreased. Comparative Example 1 lacked a photothermal carrier but retained the modified liquid, and its selectivity was slightly higher than that of Comparative Examples 2 and 4.

[0052] Product yield testing: The reaction was carried out according to the above "methane activation capacity and formaldehyde selectivity test". The catalysts prepared in Example 1 and Comparative Example 1 were placed in quartz tubes, and the yields of CH3OH, HCHO, CO2, and CO were analyzed. The product yields were calculated as follows: In the formula, n is the amount of substance (μmol) of the products (HCHO, CO2, CO). t is the reaction time (h).

[0053] See results Figure 3 As shown, it is a schematic diagram of the product yield of Example 1 and Comparative Example 1. It can be seen that the HCHO yield of Example 1 is much higher than that of Comparative Example 1, and the formaldehyde selectivity is higher.

[0054] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a catalyst for photo-thermal catalytic conversion of methane to formaldehyde in a gas-solid continuous flow, characterized in that, It includes the following steps: S1. Preparation of pretreated carrier: The composite carrier was dispersed in deionized water, ultrasonically dispersed for 15-20 min, and then dried at 105-110℃ to obtain the pretreated carrier. S2. Preparation of precursor solution: S201. Disperse ZnO in deionized water at a mass ratio of 1:5 to obtain a zinc oxide suspension; Palladium chloride solution was added to zinc oxide suspension, stirred at room temperature for 1-2 hours, vacuum filtered, washed and dried to obtain Pd / ZnO precursor; The Pd loading is 2-3 wt% relative to the ZnO mass. S202. Disperse the Pd / ZnO precursor in deionized water and sonicate for 15-20 min to form a Pd / ZnO dispersion. Weigh rare earth metal salts according to the Pd:X molar ratio of 1:(0.4-0.5) and add them to the Pd / ZnO dispersion. Stir for 20-25 min. Add triethylenetetramine dropwise to adjust the pH to 7.5-8, stir, add sodium hypophosphite, and continue stirring for 30-40 minutes to obtain the precursor solution; X is selected from Ce and La, and the mass ratio of sodium hypophosphite to Pd / ZnO precursor is 1:(1.5~2); S3. Preparation of composite precursor: The pretreated carrier was added to the precursor solution, vacuum impregnated for 3-4 hours, and dried to obtain the loaded precursor. The loaded precursor was placed in a tube furnace, H2 was introduced, and the temperature was raised to 400~450℃ at room temperature and held for 4.5~7h to obtain the composite precursor. S4. Post-processing: The composite precursor was immersed in the modified liquid, stirred at room temperature for 1 hour, ultrasonically dispersed for 10-15 minutes, filtered, dried at 75-80℃ for 4-6 hours, and then calcined at 150-160℃ for 0.5-1 hour under nitrogen protection to obtain a gas-solid continuous flow photothermal catalytic catalyst for the production of formaldehyde from methane. The modified solution comprises catechol resin, γ-aminopropyltriethoxysilane, acetylacetone, and ethanol solution in a mass ratio of 2:1:(0.5~0.7):

20.

2. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 1, characterized in that: The composite carrier comprises a photothermal carrier and a structural reinforcement carrier in a mass ratio of 1:(1~2); The method for preparing the photothermal carrier includes the following steps: Biochar and boron mud were mixed in a mass ratio of 3:2, impregnated in a 5wt% hydrochloric acid solution for 25-30 minutes, washed until neutral, and dried at 105-110℃ to obtain a composite matrix. The composite matrix is ​​mixed with nickel phosphide and ground in a ball mill for 1.5-2 hours to obtain a photothermal carrier; The mass ratio of the boron mud to nickel phosphide is 1:(0.2~0.5); The method for preparing the structural reinforcement carrier includes the following steps: Diatomaceous earth and perlite were mixed at a mass ratio of 4:(2~3) and dried at 110~120℃ for 3~4 hours. The mixture was then dispersed in a sodium gellan gum aqueous solution at 80℃, stirred for 1 hour, and dried at 100~105℃ for 2~3 hours to obtain a structural reinforcement carrier.

3. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 2, characterized in that: The concentration of the sodium gellan gum aqueous solution is 8~10wt%.

4. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 2, characterized in that: The method for preparing the biochar includes the following steps: After crushing the straw to 0.5~2mm, it is placed in a closed carbonization furnace and heated to 500~550℃ at a rate of 10℃ / min under nitrogen protection. The carbonization is carried out at a constant temperature for 2~3 hours and then cooled to room temperature to obtain biochar.

5. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 1, characterized in that: In S202, the rare earth metal salt is selected from either cerium nitrate or lanthanum nitrate.

6. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 1, characterized in that: In step S3, heating to 400-450°C at room temperature and holding at that temperature for 4.5-7 hours includes the following steps: The temperature was raised from room temperature to 260℃ and held for 1.5~2 hours at a rate of 2℃ / min. The temperature is increased from 260℃ to 400~450℃ and held for 3~5 hours, with a heating rate of 5℃ / min.

7. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 1, characterized in that: In S3, the H2 flow rate is 80 mL / min.

8. The method for preparing the catalyst for photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in claim 1, characterized in that: In the ethanol solution of the modified liquid, the mass ratio of anhydrous ethanol to deionized water is 3:

1.

9. A catalyst for the photothermal catalytic production of formaldehyde from methane in a continuous gas-solid flow, characterized in that, It is prepared by the method for preparing the catalyst for the photothermal catalytic production of formaldehyde from methane under continuous gas-solid flow as described in any one of claims 1 to 8.

10. The application of the catalyst for the photothermal catalytic conversion of methane to formaldehyde under continuous gas-solid flow as described in claim 9 in the direct conversion of methane to formaldehyde under continuous gas-solid flow photothermal catalytic flow.

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