Preparation method and application of HPW and Ru co-modified CeO2 porous nanorod catalyst

Abstract

The invention discloses a preparation method and application of an HPW and Ru co-modified CeO2 porous nanorod catalyst, and belongs to the technical field of catalytic materials. The method comprises the following steps: (1) preparing cerium dioxide porous nanorods; (2) loading HPW on the cerium dioxide porous nanorod to obtain CeO2-HPW; and (3) loading Ru nano particles on the CeO2-HPW, so as to obtain the CeO2 porous nanorod catalyst Ru / CeO2-HPW co-modified by the HPW and the Ru. The catalyst disclosed by the invention is of a porous rod-like structure and has the characteristics of high pore diameter, high acid capacity, multiple oxidation-reduction active sites, water vapor resistance and the like. The catalyst disclosed by the invention is applied to the catalytic oxidation reaction of 1, 2-DCE, and shows excellent catalytic performance at 90% conversion rate temperature T90 of 273 DEG C, the carbon dioxide mineralization rate of 1, 2-DCE reaches 90% at 279 DEG C, and the generation of by-products is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst materials, and particularly relates to a preparation method and application of a catalyst of HPW and Ru co-modified CeO2 porous nanorods. Background Art

[0002] Chlorinated volatile organic compounds (CVOCs) are highly volatile, chemically stable, and toxic chlorinated hydrocarbons. 1,2-Dichloroethane (DCE) is a typical CVOC, which is widely used in many industries such as pharmaceuticals, coatings, printing, and petrochemicals. Common methods for treating CVOCs include adsorption, absorption, condensation, combustion, non-thermal plasma, and catalytic oxidation. Among them, catalytic oxidation is an efficient and thorough method for eliminating CVOCs. However, the catalytic oxidation degradation of CVOCs faces challenges such as chlorine poisoning and water vapor interference, which are more difficult to solve compared with non-halogenated VOCs. Therefore, in the catalytic oxidation of CVOCs, it is crucial to explore catalysts with high activity, water vapor resistance, and chloride resistance.

[0003] CeO2 is a rare earth oxide with rich reserves, and its Ce 3+ / Ce 4+ is easy to transform into each other, endowing it with abundant oxygen vacancies and Lewis acidity. These properties make CeO2 an ideal redox carrier or active component, which is widely used in various catalytic studies. However, the original CeO2 has significant problems in catalyzing chlorinated volatile organic compounds (CVOCs): First, inorganic chlorine (Cl) species will strongly occupy the surface oxygen vacancies, resulting in catalyst deactivation. Second, the oxygen storage capacity (OSC) and the concentration of surface oxygen vacancies of pure CeO2 are relatively low, and the redox ability is insufficient, making it difficult to efficiently activate CVOCs molecules. Usually, a relatively high temperature is required to achieve complete oxidation, with high energy consumption and easy chlorine poisoning. In addition, the Cl - released during the decomposition of CVOCs will strongly adsorb on the surface of CeO2, forming stable Ce-Cl bonds, covering the active oxygen vacancies, and further exacerbating catalyst deactivation. The accumulation of Cl - may also trigger secondary reactions, generating highly toxic polychlorinated by-products or Cl2, reducing the reaction selectivity and safety. At the same time, under high-temperature reaction conditions (especially in a Cl-containing environment), CeO2 is prone to grain agglomeration and sintering, resulting in a decrease in specific surface area and a reduction in active sites, further weakening its catalytic performance.

[0004] Ruthenium (Ru) is a noble metal, which has been applied in many studies on the catalytic oxidation of chlorinated volatile organic compounds (CVOCs) due to its excellent activity in the Deacon reaction and outstanding chlorine treatment ability. However, RuO xThe high redox performance (or high Deacon reaction activity) of CeO2 will inevitably lead to the formation of a large amount of Cl2, thus promoting further chlorination during the catalytic oxidation of CVOCs and generating more polychlorinated organic compounds (polychlorinated by-products). Summary of the Invention

[0005] Aiming at the deficiencies in the above-mentioned prior art, the present invention provides a preparation method and application of a HPW and Ru co-modified CeO2 porous nanorod catalyst. The catalyst is obtained by loading phosphotungstic acid and ruthenium on cerium dioxide porous nanorods. The catalyst has a porous rod-like structure, high pore diameter, high acid capacity, many redox active sites, water vapor resistance, and good catalytic performance in the 1,2-DCE reaction.

[0006] In order to achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A preparation method of a HPW and Ru co-modified CeO2 porous nanorod catalyst includes the following steps: preparing cerium dioxide CeO2 porous nanorods, adding the CeO2 porous nanorods to an aqueous solution of phosphotungstic acid HPW and stirring for reaction to prepare CeO2-HPW, and then loading Ru nanoparticles to obtain the HPW and Ru co-modified CeO2 porous nanorod catalyst.

[0008] Further, the preparation method of the HPW and Ru co-modified CeO2 porous nanorod catalyst specifically includes the following steps:

[0009] (1) Preparation of cerium dioxide porous nanorods: Cerium dioxide porous nanorods are prepared by a hydrothermal method, denoted as CeO2.

[0010] (2) Preparation of CeO2-HPW: Immerse the cerium dioxide porous nanorods in step (1) into an aqueous solution of HPW with a mass concentration of 10-15 g / L, stir at room temperature for 10-15 h, then centrifuge, wash the precipitate, dry, and calcine to obtain CeO2-HPW; put the cerium dioxide porous nanorods into a phosphotungstic acid solution for phosphotungstic acid loading. Phosphotungstic acid (H3PW 12 O 40 , HPW) dissociates into heteropolyanions [PW 12 O 40 3- ​, its unique Keggin structure (the central PO4 tetrahedron is surrounded by 12 WO6 octahedra) endows it with strong acidity and redox activity; porous CeO2 (PN-CeO2) undergoes electrostatic adsorption or hydrogen bonding with HPW anions through its high specific surface area and surface hydroxyl groups (-OH); the mesoporous structure of CeO2 promotes the uniform dispersion of HPW and prevents aggregation; at high temperatures, HPW may partially decompose into WO3 and P2O5, but the core of the Keggin structure ([PW 12 O 40 3- ) can be retained and covalently bonded to the CeO2 lattice to form a W-O-Ce interface; the remaining WO3 forms a composite oxide with CeO2, enhancing the thermal stability.

[0011] (3) Synthesis of Ru / CeO2-HPW: Ultrasonically disperse the CeO2-HPW from step (2) in water, then add a mixed solution of RuCl3·3H2O, isopropanol, and water to form a suspension. Adjust the pH of the suspension to neutral. After stirring, inject the prepared aqueous NaBH4 solution into the suspension for mixing. After filtration, wash and dry the precipitate. Transfer the dried powder into a tubular furnace and introduce a H2 / Ar mixed gas for reaction to obtain a HPW and Ru co-modified CeO2 porous nanorod catalyst, denoted as Ru / CeO2-HPW. During this process, when the pH is neutral, the surface of CeO2 is positively charged, and [Ru(H2O)6] 3+ is adsorbed through electrostatic interaction. The hydroxyl groups (-OH) on the surface of CeO2 and the heteropolyanions of HPW ([PW 12 O 40 3- ) form coordination bonds with Ru 3+ , enhancing the metal-support interaction; NaBH4 rapidly reduces Ru 3+ to metallic Ru 0 under neutral pH conditions; isopropanol can reduce the polarity of the aqueous solution, slow down the nucleation rate of Ru NPs, and inhibit particle aggregation; in the subsequent reaction in a 5% H2 / Ar atmosphere, the residual Cl in RuCl is reduced, reducing the influence of the residual Cl on the catalytic activity of the catalyst; it promotes the desorption of Cl - and purifies the catalyst surface.

[0012] ​​Further, in step (1), an aqueous solution of Ce(NO3)3·6H2O is mixed with an aqueous solution of NaOH. After stirring, a first hydrothermal reaction is carried out. After the reaction ends, it is naturally cooled to room temperature, centrifuged, and the precipitate is collected to obtain a first product. The first product is washed and dried. The dried product is then added to water and a second hydrothermal reaction is carried out. After the reaction ends, a second product is formed. The second product is calcined to obtain cerium dioxide porous nanorods, denoted as CeO2. The weight ratio of Ce(NO3)3·6H2O to NaOH is 1-2:18-20. The temperature of the first hydrothermal reaction is 90-110 °C and the time is 20-30 h. The temperature of the second hydrothermal reaction is 150-180 °C and the time is 10-15 h. The calcination conditions are as follows: heating at a rate of 5 °C / min, the calcination temperature is 450-550 °C, and the calcination time is 1-3 h. By setting the hydrothermal conditions, amorphous cerium hydroxide is promoted to dehydrate and crystallize to form CeO2 nanoparticles with a cubic fluorite structure. The secondary hydrothermal treatment at a higher temperature promotes Ostwald ripening of the particles, small particles dissolve and recrystallize on the surface of large particles, forming a more stable porous structure. Calcination removes residual hydroxyl groups and organic substances, further improving the crystallinity of CeO2 and stabilizing the porous structure.

[0013] Further, in step (2), the calcination conditions are as follows: heating at a rate of 5 °C / min, the calcination temperature is 450-550 °C, and the calcination time is 1-3 h.

[0014] Further, the specific operation steps of step (3) are as follows: 0.3-0.5 g of CeO2-HPW obtained in step (2) is ultrasonically dispersed in 90-110 mL of water for 20-50 min to obtain a suspension. After mixing 1-3 mL of isopropanol and 15-20 mL of water, 0.01-0.02 g of RuCl3·3H2O is added and mixed evenly to obtain a mixed solution. The mixed solution is added to the suspension and mixed evenly to form a suspension. The pH of the suspension is adjusted to neutral, and after stirring for 20-50 min, 7-9 mL of a 10 mM aqueous solution of NaBH4 prepared is injected into the suspension and mixed. After filtration, the precipitate is washed and dried. The dried powder is transferred into a tubular furnace, and a 5% H2 / Ar mixed gas is introduced, and the reaction is carried out at 200-300 °C for 1-3 h to obtain a HPW and Ru co-modified CeO2 porous nanorod catalyst, denoted as Ru / CeO2-HPW.

[0015] Further, the HPW and Ru co-modified CeO2 porous nanorod catalyst has a porous structure, a specific surface area of 75-76 m 2 / g, and a pore volume of 0.35-0.40 cm 3 / g, with an average pore diameter of 24.0 - 24.5 nm and a total acid amount of 430 - 450 μmol / g; in the catalytic oxidation reaction of 1,2-DCE, the temperature T corresponding to 90% conversion rate in the HPW and Ru co-modified CeO2 porous nanorod catalysis 90 is 270 - 275 °C.

[0016] The present invention also provides the application of the HPW and Ru co-modified CeO2 porous nanorod catalyst in the reaction of catalytically treating chlorinated volatile organic compounds.

[0017] Furthermore, the chlorinated volatile organic compound is 1,2-dichloroethane, i.e., 1,2-DCE.

[0018] Furthermore, the application of the HPW and Ru co-modified CeO2 porous nanorod catalyst in the reaction of catalytically treating chlorinated volatile organic compounds includes the following steps: loading 150 - 250 mg of the HPW and Ru co-modified CeO2 porous nanorod catalyst into a reactor, introducing 1,2-DCE into the reactor, and the introduction concentration of the 1,2-DCE is 900 - 1200 ppm; simultaneously introducing a mixed gas of nitrogen and oxygen, the total flow rate of the mixed gas is 100 mL / min, and the content of oxygen is 10% by volume fraction.

[0019] The present invention has the following beneficial effects:

[0020] 1. The present invention prepares porous nanorod cerium dioxide by a two-step hydrothermal method, loads phosphotungstic acid on the obtained cerium dioxide, and then loads ruthenium nanoparticles on the precursor. After treatment with 5% H2 / Ar, a porous nanorod cerium dioxide catalyst co-modified with phosphotungstic acid and ruthenium nanoparticles is obtained; the catalyst has a porous structure, a specific surface area of 75.15 m 2 / g, a pore volume of 0.390 cm 3 / g, an average pore diameter of 24.17 nm, a high pore diameter, and many active sites, and has good catalytic performance in chlorinated volatile organic compounds (CVOCs) such as 1,2-DCE.

[0021] 2. The secondary hydrothermal reaction of the present invention forms porous structure cerium dioxide and loads phosphotungstic acid, which together provide an electron transfer channel, promoting the high dispersion and stability of RuNPs; adding NaBH4 for reaction to achieve small-sized and highly dispersed RuNPs; the synergy of the redox property of CeO2, the acidity of HPW, and the metal activity of Ru forms a multifunctional catalytic interface, which can provide more catalytic active sites for the 1,2-DCE reaction.

[0022] 3. Applying the catalyst of the present invention to the catalytic oxidation reaction of 1,2-DCE, the temperature T at 90% conversion rate 90The temperature is 273 °C, showing excellent catalytic performance. The Ru loading is beneficial to the generation of Ru-O-Ce bonding, enhancing the activity and migration ability of oxygen species; the carbon dioxide mineralization rate of 1,2-DCE reaches 90% at 279 °C, reducing the generation of by-products. The loading of HPW generates a large number of acidic sites, especially The acidic sites are conducive to the generation of HCl. The synergistic effect of acidic sites and active sites jointly promotes the catalytic degradation of 1,2-DCE and inhibits the generation of polychlorinated by-products, showing good industrial application potential. Brief Description of the Drawings

[0023] Figure 1 XRD patterns of Ru / CeO2-HPW, CeO2, CeO2-HPW and Ru / CeO2 prepared in Example 1, Comparative Example 1-3 respectively.

[0024] Figure 2 TEM image of Ru / CeO2-HPW prepared in Example 1.

[0025] Figure 3 EDS elemental distribution map of Ru / CeO2-HPW prepared in Example 1.

[0026] Figure 4 XPS spectrum of Ru / CeO2-HPW prepared in Example 1;

[0027] Figure 5 N2 adsorption-desorption isotherm and pore size distribution curve of Ru / CeO2-HPW prepared in Example 1.

[0028] Figure 6 1,2-DCE conversion rate and carbon dioxide yield of Ru / CeO2-HPW, CeO2, CeO2-HPW, Ru / CeO2 and Ru / CeO2-HPW(air) in Application Example 1, Application Comparative Example 1-4.

[0029] Figure 7 Results of 1 vol% water vapor 24-hour durability test of Ru / CeO2-HPW prepared in Example 1. Detailed Embodiments

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] A preparation method of a HPW and Ru co-modified CeO2 porous nanorod catalyst, comprising the following steps:

[0033] (1) Preparation of cerium dioxide porous nanorods: An aqueous solution of Ce(NO3)3·6H2O (1.736 g, dissolved in 10 ml of deionized water) was mixed with an aqueous solution of NaOH (19.2 g, dissolved in 70 mL of deionized water). Under continuous stirring, the mixture was aged for 30 min, and then the first hydrothermal reaction was carried out at 100 °C for 24 h. After the reaction ended, it was naturally cooled to room temperature, centrifuged, and the precipitate was collected to obtain the first product. The first product was thoroughly washed with deionized water until neutral, and then dried in an oven at 60 °C. 1 g of the dried product was added to 80 mL of water and the second hydrothermal reaction was carried out. The hydrothermal treatment was carried out at 160 °C for 12 h. After the reaction ended, the second product was formed. The second product was calcined in a muffle furnace, heated at 5 °C / min, 500 °C / 2 h, to obtain cerium dioxide porous nanorods, denoted as CeO2.

[0034] (2) Preparation of CeO2-HPW: 0.48 g of phosphotungstic acid H3PW 12 O 40 was dissolved in 40 mL of deionized water to form a 12 g / L HPW aqueous solution. Then, 0.8 g of the cerium dioxide porous nanorods CeO2 obtained in step (1) was weighed and added to the above HPW aqueous solution. Stir at room temperature for 12 h, centrifuge, wash the precipitate 3 times, and collect it by re-filtration. The obtained solid was dried in an oven at 80 °C for 12 h. Finally, it was heated at 5 °C / min and calcined at 500 °C for 2 h to prepare CeO2-HPW powder.

[0035] (3) Synthesis of Ru / CeO2-HPW: 0.4 g of the CeO2-HPW powder obtained in step (2) was ultrasonically dispersed in 100 mL of water for 30 min to obtain a suspension; after mixing 2 mL of isopropanol and 18 mL of water, 0.01034 g of RuCl3·3H2O was added and mixed well to obtain a mixed solution; the mixed solution was added to the suspension and mixed well to form a suspension. The pH of the suspension was adjusted to 7 with 0.1 M NaOH aqueous solution. After stirring for 30 min, 7.915 mL of the prepared 10 mM NaBH4 aqueous solution was injected into the suspension and mixed to react to produce a precipitate. After filtration, the precipitate was collected, washed 3 times, and dried in a vacuum oven at 60 °C for 12 h. The dried powder was loaded into a porcelain boat and then transferred to a tubular furnace, and a 5% H2 / Ar mixed gas was introduced. The reaction was carried out at 250 °C for 2 h to obtain a HPW and Ru co-modified CeO2 porous nanorod catalyst, denoted as Ru / CeO2-HPW.

[0036] Example 2

[0037] A preparation method of a HPW and Ru co-modified CeO2 porous nanorod catalyst, comprising the following steps:

[0038] (1) Preparation of cerium dioxide porous nanorods: An aqueous solution of Ce(NO3)3·6H2O (1.239 g, dissolved in 10 ml of deionized water) was mixed with an aqueous solution of NaOH (18.7 g, dissolved in 70 mL of deionized water). Under continuous stirring, the mixture was aged for 30 min, and then the first hydrothermal reaction was carried out at 95 °C for 30 h. After the reaction ended, it was naturally cooled to room temperature, centrifuged, and the precipitate was collected to obtain the first product. The first product was thoroughly washed with deionized water until neutral, and then dried in an oven at 60 °C. 1 g of the dried product was added to 80 mL of water and the second hydrothermal reaction was carried out. The hydrothermal treatment was carried out at 150 °C for 15 h. After the reaction ended, the second product was formed. The second product was calcined in a muffle furnace, heated at 5 °C / min, and calcined at 450 °C for 3 h to obtain cerium dioxide porous nanorods, denoted as CeO2.

[0039] (2) Preparation of CeO2-HPW: 0.48 g of phosphotungstic acid H3PW 12 O 40 was dissolved in 40 mL of deionized water to form a 12 g / L HPW aqueous solution. Then, 0.8 g of the cerium dioxide porous nanorods CeO2 prepared in step (1) was weighed and added to the above HPW aqueous solution. The reaction was stirred at room temperature for 10 h, and then centrifuged. The precipitate was washed 3 times and collected by re-filtration. The obtained solid was dried in an oven at 80 °C for 12 h. Finally, it was heated at 5 °C / min and calcined at 550 °C for 1 h to obtain CeO2-HPW powder.

[0040] (3) Synthesis of Ru / CeO2-HPW: 0.5 g of the CeO2-HPW powder prepared in step (2) was ultrasonically dispersed in 110 mL of water for 50 min to obtain a suspension; after mixing 3 mL of isopropanol and 20 mL of water, 0.02 g of RuCl3·3H2O was added and mixed well to obtain a mixed solution; the mixed solution was added to the suspension and mixed well to form a suspension. The pH of the suspension was adjusted to neutral, stirred for 40 min, and then 9 mL of a 10 mM NaBH4 aqueous solution prepared was injected into the suspension and mixed. After filtration, the precipitate was washed and dried. The dried powder was transferred into a tubular furnace and a 5% H2 / Ar mixed gas was introduced. The reaction was carried out at 300 °C for 1.5 h to obtain a catalyst of HPW and Ru co-modified CeO2 porous nanorods, denoted as Ru / CeO2-HPW.

[0041] Example 3

[0042] A preparation method of a catalyst of HPW and Ru co-modified CeO2 porous nanorods, comprising the following steps:

[0043] (1) Preparation of cerium dioxide porous nanorods: An aqueous solution of Ce(NO3)3·6H2O (2.000 g, dissolved in 10 ml of deionized water) was mixed with an aqueous solution of NaOH (19.8 g, dissolved in 70 mL of deionized water). Under continuous stirring, the mixture was aged for 30 min, and then the first hydrothermal reaction was carried out at 110 °C for 20 h. After the reaction ended, it was naturally cooled to room temperature, centrifuged, and the precipitate was collected to obtain the first product. The first product was thoroughly washed with deionized water until neutral, and then dried in an oven at 60 °C. 1 g of the dried product was added to 80 mL of water and the second hydrothermal reaction was carried out. The hydrothermal treatment was carried out at 180 °C for 10 h. After the reaction ended, the second product was formed. The second product was calcined in a muffle furnace, heated at 5 °C / min, 550 °C / 1 h, to obtain cerium dioxide porous nanorods, denoted as CeO2.

[0044] (2) Preparation of CeO2-HPW: 0.48 g of phosphotungstic acid H3PW 12 O 40 was dissolved in 40 mL of deionized water to form a 12 g / L HPW aqueous solution. Then, 0.8 g of the cerium dioxide porous nanorods CeO2 from step (1) was weighed and added to the above HPW aqueous solution. The reaction was stirred at room temperature for 15 h, and then centrifuged. The precipitate was washed 3 times and collected by re-filtration. The obtained solid was dried in an oven at 80 °C for 12 h. Finally, it was heated at 5 °C / min and calcined at 450 °C for 3 h to obtain CeO2-HPW powder.

[0045] (3) Synthesis of Ru / CeO2-HPW: 0.3 g of the CeO2-HPW powder from step (2) was ultrasonically dispersed in 90 mL of water for 20 min to obtain a suspension; 1 mL of isopropanol and 15 mL of water were mixed evenly, and then 0.01 g of RuCl3·3H2O was added and mixed evenly to obtain a mixed solution; the mixed solution was added to the suspension and mixed evenly to form a suspension. The pH of the suspension was adjusted to neutral, stirred for 20 min, and then 7 mL of the prepared 10 mM NaBH4 aqueous solution was injected into the suspension and mixed. After filtration, the precipitate was washed and dried. The dried powder was transferred into a tubular furnace and a 5% H2 / Ar mixed gas was introduced. The reaction was carried out at 200 °C for 3 h to obtain a HPW and Ru co-modified CeO2 porous nanorod catalyst, denoted as Ru / CeO2-HPW.

[0046] Comparative Example 1

[0047] The difference between Comparative Example 1 and Example 1 is that the cerium dioxide porous nanorods in Comparative Example 1 were not modified with phosphotungstic acid and ruthenium nanoparticles, and the remaining preparation processes and conditions were the same as those in Example 1, and a cerium dioxide porous nanorod catalyst (CeO2) was prepared.

[0048] The specific preparation steps are as follows: Mix an aqueous solution of Ce(NO3)3·6H2O (1.736 g, dissolved in 10 ml of deionized water) with an aqueous solution of NaOH (19.2 g, dissolved in 70 mL of deionized water). Under continuous stirring, age the mixture for 30 min, then carry out the first hydrothermal reaction, react at 100 °C for 24 h. After the reaction is completed, naturally cool to room temperature, centrifuge and collect the precipitate to obtain the first product. Thoroughly wash the first product with deionized water until neutral, then dry it in an oven at 60 °C. Add 1 g of the dried product to 80 mL of water and carry out the second hydrothermal reaction, hydrothermally treat at 160 °C for 12 h. After the reaction is completed, form the second product. Calcinate the second product in a muffle furnace, heat up at 5 °C / min, 500 °C / 2 h, to obtain the cerium dioxide porous nanorod catalyst, denoted as CeO2.

[0049] Comparative Example 2

[0050] The difference between Comparative Example 2 and Example 1 is that the cerium dioxide porous nanorods in Comparative Example 2 are not modified with Ru, that is, step (3) is deleted, and the remaining preparation processes and conditions are the same as those in Example 1, to obtain the phosphotungstic acid-loaded CeO2 catalyst (denoted as CeO2-HPW). The specific preparation steps are as follows:

[0051] (1) Preparation of cerium dioxide porous nanorods: Mix an aqueous solution of Ce(NO3)3·6H2O (1.736 g, dissolved in 10 ml of deionized water) with an aqueous solution of NaOH (19.2 g, dissolved in 70 mL of deionized water). Under continuous stirring, age the mixture for 30 min, then carry out the first hydrothermal reaction, react at 100 °C for 24 h. After the reaction is completed, naturally cool to room temperature, centrifuge and collect the precipitate to obtain the first product. Thoroughly wash the first product with deionized water until neutral, then dry it in an oven at 60 °C. Add 1 g of the dried product to 80 mL of water and carry out the second hydrothermal reaction, hydrothermally treat at 160 °C for 12 h. After the reaction is completed, form the second product. Calcinate the second product in a muffle furnace, heat up at 5 °C / min, 500 °C / 2 h, to obtain the cerium dioxide porous nanorods, denoted as CeO2.

[0052] (2) Preparation of CeO2-HPW: Dissolve 0.48 g of phosphotungstic acid H3PW 12 O 40 in 40 mL of deionized water to form a 12 g / L HPW aqueous solution. Then weigh 0.8 g of the cerium dioxide porous nanorods CeO2 from step (1) and add it to the above HPW aqueous solution, stir at room temperature for 12 h, centrifuge, wash the precipitate 3 times, and collect it by re-filtration. The obtained solid is dried in an oven at 80 °C for 12 h, and finally heated up at 5 °C / min and calcined at 500 °C for 2 h to obtain the CeO2-HPW catalyst.

[0053] Comparative Example 3

[0054] The difference between Comparative Example 3 and Example 1 is that the cerium dioxide porous nanorods in Comparative Example 3 are not modified with phosphotungstic acid, and the remaining preparation processes and conditions are the same as those in Example 1, and the ruthenium nanoparticle-loaded CeO2 catalyst (denoted as Ru / CeO2) is prepared. The specific preparation steps are as follows:

[0055] (1) Preparation of cerium dioxide porous nanorods: An aqueous solution of Ce(NO3)3·6H2O (1.736 g, dissolved in 10 ml of deionized water) is mixed with an aqueous solution of NaOH (19.2 g, dissolved in 70 mL of deionized water). Under continuous stirring, the mixture is aged for 30 min, and then subjected to the first hydrothermal reaction at 100 °C for 24 h. After the reaction is completed, it is naturally cooled to room temperature, centrifuged, and the precipitate is collected to obtain the first product. The first product is thoroughly washed with deionized water until neutral, and then dried in an oven at 60 °C. 1 g of the dried product is added to 80 mL of water and subjected to the second hydrothermal reaction, and hydrothermally treated at 160 °C for 12 h. After the reaction is completed, the second product is formed. The second product is calcined in a muffle furnace, heated at 5 °C / min, and calcined at 500 °C for 2 h to obtain cerium dioxide porous nanorods, denoted as CeO2.

[0056] (2) Preparation of Ru / CeO2: 0.4 g of cerium dioxide porous nanorods are ultrasonically dispersed in 100 mL of deionized water for 30 min to obtain a suspension; 2 mL of isopropanol and 18 mL of water are mixed evenly, and then 0.01034 g of RuCl3·3H2O is added and mixed evenly to obtain a mixed solution; the mixed solution is added to the suspension and mixed evenly to form a suspension. The pH of the suspension is adjusted to 7 with 0.1 M NaOH aqueous solution. After stirring for 30 min, 7.915 mL of the prepared 10 mM NaBH4 aqueous solution is injected into the suspension and mixed. After filtration, the precipitate is washed 3 times and dried in a vacuum oven at 60 °C for 12 h. The dried powder is transferred into a tubular furnace, and a 5% H2 / Ar mixed gas is introduced and reacted at 250 °C for 2 h to obtain the Ru / CeO2 catalyst.

[0057] Comparative Example 4

[0058] The difference between Comparative Example 4 and Example 1 is that in step (3), the 5% H2 / Ar mixed gas is replaced with air, and the remaining preparation processes and conditions are the same as those in Example 1, and the phosphotungstic acid and ruthenium nanoparticle-loaded cerium dioxide catalyst (denoted as Ru / CeO2-HPW(air)) is prepared. The specific preparation steps are as follows:

[0059] (1) Preparation of cerium dioxide porous nanorods: An aqueous solution of Ce(NO3)3·6H2O (1.736 g, dissolved in 10 ml of deionized water) was mixed with an aqueous solution of NaOH (19.2 g, dissolved in 70 mL of deionized water). Under continuous stirring, the mixture was aged for 30 min, and then the first hydrothermal reaction was carried out at 100 °C for 24 h. After the reaction ended, it was naturally cooled to room temperature, centrifuged, and the precipitate was collected to obtain the first product. The first product was thoroughly washed with deionized water until neutral, and then dried in an oven at 60 °C. 1 g of the dried product was added to 80 mL of water and the second hydrothermal reaction was carried out. The hydrothermal treatment was carried out at 160 °C for 12 h. After the reaction ended, the second product was formed. The second product was calcined in a muffle furnace, heated at a rate of 5 °C / min, and calcined at 500 °C for 2 h to obtain cerium dioxide porous nanorods, denoted as CeO2.

[0060] (2) Preparation of CeO2-HPW: 0.48 g of phosphotungstic acid H3PW 12 O 40 was dissolved in 40 mL of deionized water to form a 12 g / L HPW aqueous solution. Then, 0.8 g of the cerium dioxide porous nanorods CeO2 obtained in step (1) was weighed and added to the above HPW aqueous solution. Stirring was carried out at room temperature for 12 h, centrifuged, the precipitate was washed 3 times, and collected by re-filtration. The obtained solid was dried in an oven at 80 °C for 12 h, and finally heated at a rate of 5 °C / min and calcined at 500 °C for 2 h to prepare CeO2-HPW powder.

[0061] (3) Synthesis of Ru / CeO2-HPW: 0.4 g of the CeO2-HPW powder obtained in step (2) was ultrasonically dispersed in 100 mL of water for 30 min to obtain a suspension; after mixing 2 mL of isopropanol and 18 mL of water, 0.01034 g of RuCl3·3H2O was added and mixed well to obtain a mixed solution; the mixed solution was added to the suspension and mixed well to form a suspension. The pH of the suspension was adjusted to 7 with 0.1 M NaOH aqueous solution. After stirring for 30 min, 7.915 mL of the prepared 10 mM NaBH4 aqueous solution was injected into the suspension and mixed. After filtration, the precipitate was washed 3 times and dried in a vacuum oven at 60 °C for 12 h. The dried powder was loaded into a porcelain boat and then transferred to a tubular furnace, and air was introduced. The reaction was carried out at 250 °C for 2 h to obtain a CeO2 porous nanorod catalyst co-modified with HPW and Ru, denoted as Ru / CeO2-HPW(air).

[0062] The characterization and analysis of the prepared catalyst materials are as follows:

[0063] (I) X-ray diffraction (XRD) analysis

[0064] The Ru / CeO2-HPW, CeO2, CeO2-HPW, and Ru / CeO2 prepared in Example 1 and Comparative Examples 1-3 were characterized by X-ray diffractometer (XRD) to reveal the crystal structures of the prepared samples. The characterization results are as Figure 1 shown. It can be seen from Figure 1 that the loading of HPW, Ru, or HPW and Ru has no obvious effect on the phase composition and crystal structure of the final samples. All CeO2-based catalysts show characteristic diffraction peaks of cubic fluorite structure CeO2 (PDF#34-0394) at 28.6°, 33.3°, 47.5°, 56.5°, and 59.2°, but no crystalline phase peaks of Ru or HPW are detected, confirming that Ru and HPW exist in the form of amorphous or highly dispersed nanoparticles. This highly dispersed property helps the active sites of the catalyst to be more fully exposed to the reactants, thereby enhancing its catalytic performance.

[0065] (II) Transmission electron microscopy (TEM) analysis

[0066] The Ru / CeO2-HPW prepared in Example 1 was characterized by scanning electron microscopy (TEM). The characterization results are as Figure 2 shown. High-resolution TEM (HR-TEM) was used to analyze the morphological characteristics of cerium oxide loaded with different phosphotungstic acids and ruthenium. The results show that the overall morphology of the cerium oxide loaded with phosphotungstic acid and ruthenium is not changed, and the cerium oxide is still mainly in the form of porous nanorods. This indicates that the introduced phosphotungstic acid and ruthenium species are highly dispersed on CeO2 and do not change the crystal structure of CeO2, which can significantly increase the exposure density of the active sites on the catalyst surface. At the same time, the porous nanorod structure provides a high specific surface area and rich mass transfer channels, which is beneficial to the adsorption of reactant molecules and the diffusion of intermediate products. These structural characteristics may synergistically enhance the catalytic activity and stability.

[0067] (III) Energy dispersive spectroscopy (EDS) analysis

[0068] The structure, composition, and elemental distribution on the surface of the Ru / CeO2-HPW catalyst prepared in Example 1 were studied by EDS elemental mapping. As Figure 3 shown, no aggregated particles of Ru or HPW species were directly observed. However, the presence of P, W, and Ru elements can be confirmed by elemental surface scan analysis, indicating that these species are uniformly distributed on the catalyst surface in the form of highly dispersed nanoparticles. This highly dispersed property helps to increase the contact area between the reactants and the catalyst, improve the efficiency of the catalytic reaction, and thus may increase the conversion rate.

[0069] (IV) X-ray photoelectron spectroscopy (XPS) analysis

[0070] The Ru / CeO2-HPW prepared in Example 1 was analyzed by X-ray photoelectron spectroscopy. As Figure 4As shown, it can be concluded that after-treatment with a 5% H2 / Ar mixed gas results in less residual Cl in RuCl, reducing the impact of residual Cl on the catalytic activity of the catalyst and thus increasing the conversion rate of CVOCs. Using other gases such as air does not achieve this effect.

[0071] (V) Specific surface area and pore size analysis

[0072] The specific surface area and pore size of the Ru / CeO2-HPW prepared in Example 1 were analyzed, and the results are as Figure 5 shown. From Figure 5 (a), a typical Type IV adsorption isotherm and H1 hysteresis loop can be observed, which are characteristics of a mesoporous structure; its BET area reaches 75.15 m 2 / g, the pore volume is 0.390 cm 3 / g, and the average pore diameter is 24.17 nm, which can provide active sites exposed during the catalytic reaction of 1,2-dichloroethane by the catalyst. Figure 5 (b) shows that the pore size of Ru / CeO2-HPW is mainly distributed in mesopores, and there are also macropores and micropores; this porous structure can provide more reaction sites for 1,2-dichloroethane and improve the molecular diffusion efficiency; the formation of a certain surface area and porous structure can improve the catalytic activity of the 1,2-dichloroethane reaction and accelerate electron migration.

[0073] Application examples

[0074] The catalyst samples prepared in Example 1 (Ru / CeO2-HPW), Comparative Example 1 (CeO2), Comparative Example 2 (CeO2-HPW), Comparative Example 3 (Ru / CeO2), and Comparative Example 4 (Ru / CeO2-HPW(air)) were applied to the catalytic oxidation reaction of CVOCs, and the steps are as follows:

[0075] A quartz tube with an outer diameter of 10 mm and an inner diameter of 8 mm was used as the catalytic reactor. 200 mg of the catalyst sample was loaded into the quartz reaction tube, quartz wool was plugged at both ends, and it was placed in an electric heating furnace with temperature control equipment for the activity test of the catalyst. An online GC-MS (Agilent, USA) was used to analyze various components in the tail gas, and high-purity nitrogen was used as the carrier gas for GC-MS. 1,2-DCE was introduced into the reaction system by bubbling with high-purity nitrogen (concentration about 1000 ppm), and then by controlling the flow rates of high-purity nitrogen and pure oxygen, the total gas flow rate was made 100 mL / min, the oxygen content was 10% by volume fraction, and the space velocity was 30000 mL / (g·h).

[0076] The experimental results are as Figure 6As shown in (a) and 6(c), the conversion rate of 1,2-DCE by Ru / CeO2-HPW of Example 1 was 90% at 273 °C; CeO2 of Comparative Example 1 required a temperature of 346 °C for the conversion rate of 1,2-DCE to be 90%; CeO2-HPW of Comparative Example 2 required a temperature of 274 °C for the conversion rate of 1,2-DCE to be 90%; Ru / CeO2 of Comparative Example 3 required a temperature of 299 °C for the conversion rate of 1,2-DCE to be 90%; Ru / CeO2-HPW(air) of Comparative Example 4 required a temperature of 342 °C for the conversion rate of 1,2-DCE to be 90%.

[0077] Analysis of the catalytic performance of materials

[0078] For the CeO2, CeO2-HPW, Ru / CeO 2、 Ru / CeO2-HPW and Ru / CeO2-HPW(air) catalysts used in Application Example 1 and Application Comparative Examples 1-4, the catalytic performance was analyzed. By Figure 6 (a), the performance of each catalyst for the catalytic combustion of 1,2-dichloroethane (DCE) was evaluated. The T 90 values (temperatures corresponding to 90% conversion rate) of each catalyst were in turn: Ru / CeO2-HPW (273 °C) < CeO2-HPW (274 °C) < Ru / CeO2 (299 °C) < Ru / CeO2-HPW(air) (342 °C) < CeO2 (346 °C). Compared with unmodified CeO2, all HPW (phosphotungstic acid)-modified catalysts showed better activity. The pure CeO2 support showed poor catalytic oxidation and mineralization ability ( Figure 6 (b)), while after introducing HPW, although CeO2-HPW could achieve 90% DCE conversion rate at 274 °C, its CO2 yield was low and it was not completely mineralized even at 500 °C. In addition, after loading ruthenium (Ru), the mineralization ability of the Ru / CeO2-HPW catalyst was significantly improved, and the CO2 yield reached 90% at 279 °C. Although the Ru / CeO2 catalyst had excellent redox performance, due to the lack of acidic sites, its DCE catalytic activity was still low. Compared with the Ru / CeO2-HPW catalyst, the performance of the Ru / CeO2-HPW(air) catalyst decreased because under high-temperature reaction conditions (especially in a Cl-containing environment), CeO2 was prone to grain agglomeration and sintering, resulting in a reduction in active sites. Therefore, Ru / CeO2-HPW achieved a significant improvement in the catalytic activity of 1,2-DCE by synergistically optimizing the redox performance and surface acidity.

[0079] To explore the influence of water vapor on the stability of the catalyst prepared by the present invention, a 24-hour durability experiment was carried out on the Ru / CeO2-HPW catalyst prepared in Example 1 under the condition of containing 1 vol% water vapor. The results are as Figure 7It shows that the conversion rate of 1,2-DCE of Ru / CeO2-HPW always remains at about 90%. The above results confirm that the Ru / CeO2-HPW catalyst can still maintain excellent durability in a humid environment.

[0080] In summary, the HPW and Ru co-modified CeO2 porous nanorod catalyst prepared in the present invention exists in the form of amorphous or highly dispersed nanoparticles. This highly dispersed characteristic helps the active sites of the catalyst to be more fully exposed to the reactants, thereby improving its catalytic performance. Due to the synergistic effect of the single tungstic acid structure (WO5) and the Ru-O-Ce bond, the Ru / CeO2-HPW catalyst exhibits a higher oxygen vacancy concentration, thus significantly improving its redox performance. The loading of HPW and Ru improves the catalytic activity and deep oxidation ability of the catalyst. The T 90 temperature of the Ru / CeO2-HPW catalyst is 273 °C, which is 58 °C lower than that of the CeO2 catalyst. The mineralization rate of 1,2-DCE reaches 90% at 279 °C, reducing the generation of by-products.

[0081] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be defined by the claims.

Claims

1. A preparation method of an HPW and Ru co-modified CeO2 porous nanorod catalyst, characterized in that, It includes the following steps: preparing cerium dioxide porous nanorods, adding the cerium dioxide porous nanorods into an aqueous solution of phosphotungstic acid HPW for stirring reaction to prepare CeO2-HPW, and then loading Ru to obtain a catalyst of HPW and Ru co-modified cerium dioxide porous nanorods.

2. The preparation method of an HPW and Ru co-modified CeO2 porous nanorod catalyst according to claim 1, characterized in that, Specifically, it includes the following steps: (1) Preparation of cerium dioxide porous nanorods: Cerium dioxide porous nanorods are prepared by a hydrothermal method, denoted as CeO2; (2) Preparation of CeO2-HPW: The cerium dioxide porous nanorods obtained in step (1) are immersed in an aqueous solution of HPW with a mass concentration of 10 - 15 g / L, stirred at room temperature for 10 - 15 h, then centrifuged, the precipitate is washed, dried, and calcined to obtain CeO2-HPW; (3) Synthesis of Ru / CeO2-HPW: The CeO2-HPW obtained in step (2) is ultrasonically dispersed in water, and then a mixed solution of RuCl3·3H2O, isopropanol, and water is added to form a suspension. The pH of the suspension is adjusted to neutral. After stirring, an aqueous solution of NaBH4 is injected into the suspension for mixing. After filtration, the precipitate is washed and dried. The dried powder is transferred into a tubular furnace and reacted by introducing a H2 / Ar mixed gas to obtain a catalyst of HPW and Ru co-modified cerium dioxide porous nanorods, denoted as Ru / CeO2-HPW.

3. The preparation method of an HPW and Ru co-modified CeO2 porous nanorod catalyst according to claim 2, characterized in that, The specific operation steps of step (1) are as follows: An aqueous solution of Ce(NO3)3·6H2O and an aqueous solution of NaOH are mixed. After stirring, a first hydrothermal reaction is carried out. After the reaction ends, it is naturally cooled to room temperature, centrifuged, and the precipitate is collected to obtain a first product. The first product is washed and dried. The dried product is continued to be added to water and a second hydrothermal reaction is carried out. After the reaction ends, a second product is formed. The second product is calcined to obtain cerium dioxide porous nanorods, denoted as CeO2; The weight ratio of Ce(NO3)3·6H2O to NaOH is 1 - 2:18 - 20; The temperature of the first hydrothermal reaction is 90 - 110 °C and the time is 20 - 30 h; The temperature of the second hydrothermal reaction is 150 - 180 °C and the time is 10 - 15 h; The calcination conditions are as follows: heating at 5 °C / min, the calcination temperature is 450 - 550 °C, and the calcination time is 1 - 3 h.

4. The preparation method of an HPW and Ru co-modified CeO2 porous nanorod catalyst according to claim 2, characterized in that: In step (2), the calcination conditions are as follows: heating at 5 °C / min, the calcination temperature is 450 - 550 °C, and the calcination time is 1 - 3 h.

5. The preparation method of an HPW and Ru co-modified CeO2 porous nanorod catalyst according to claim 2, characterized in that, The specific operation steps of step (3) are as follows: Ultrasonically disperse 0.3 - 0.5 g of CeO2-HPW obtained in step (2) in 90 - 110 mL of water for 20 - 50 min to obtain a suspension; mix 1 - 3 mL of isopropanol and 15 - 20 mL of water, and then add 0.01 - 0.02 g of RuCl3·3H2O and mix well to obtain a mixed solution; add the mixed solution to the suspension and mix well to form a suspension, adjust the pH of the suspension to neutral, stir for 20 - 50 min, then inject 7 - 9 mL of the prepared 10 mM NaBH4 aqueous solution into the suspension and mix, filter, wash and dry the precipitate, transfer the dried powder into a tubular furnace, introduce a 5% H2 / Ar mixed gas, and react at 200 - 300 °C for 1 - 3 h to obtain an HPW and Ru co-modified CeO2 porous nanorod catalyst, denoted as Ru / CeO2-HPW.

6. The HPW and Ru co-modified CeO2 porous nanorod catalyst prepared by the preparation method according to any one of claims 1-5, characterized in that: The HPW and Ru co-modified CeO2 porous nanorod catalyst has a porous structure, with a specific surface area of 75 - 76 m 2 / g, a pore volume of 0.35 - 0.40 cm 3 / g, an average pore diameter of 24.0 - 24.5 nm, and a total acid amount of 430 - 450 umol / g.

7. Application of the HPW and Ru co-modified CeO2 porous nanorod catalyst according to claim 6 in the reaction of catalytically degrading chlorinated volatile organic compounds.

8. The application according to claim 7, wherein: The chlorine-containing volatile organic compound is 1,2-dichloroethane; in the catalytic oxidation reaction of 1,2-dichloroethane, the T 90 emperature of the HPW and Ru co-modified CeO2 porous nanorod catalyst is 270-275 °C.

9. The application according to claim 8, characterized in that, It includes the following steps: Load 150 - 250 mg of the HPW and Ru co-modified CeO2 porous nanorod catalyst into a reactor, introduce 1,2-dichloroethane into the reactor, and the inlet concentration of the 1,2-dichloroethane is 900 - 1200 ppm; simultaneously introduce a mixed gas of nitrogen and oxygen, the total flow rate of the mixed gas is 100 mL / min, and the content of oxygen is 10% by volume fraction.

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