A rubidium-doped cerium oxide-copper oxide composite catalytic material, a preparation method and application thereof

Abstract

The application discloses a kind of rubidium-doped cerium oxide-copper composite catalytic materials and its preparation method and application, belong to catalytic technical field.Rubidium-doped cerium oxide-copper composite catalytic material is constituted by rubidium-doped in copper-cerium composite material surface, the copper-cerium composite material is constituted by copper oxide nanoparticles growth on cerium oxide nanorod, its preparation method is: first by hydrothermal method obtains cerium oxide nanorod, then in situ growth copper oxide nanoparticles on cerium oxide nanorod, then dope rubidium.The preparation method step is simple, low in cost, easy to realize large-scale production, and the catalytic material has the advantages, such as specificity is high, conversion rate is good, stable and long service life, etc., it is applied to catalytic aniline oxidation synthesis oxidation azo compound, and shows high catalytic activity, good selectivity, low cost, environment-friendly and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of cerium oxide-copper oxide composite catalytic materials doped with rubidium, specifically relates to a kind of cerium oxide nanorod loaded copper oxide nanoparticle composite catalytic materials doped with rubidium, also relates to its preparation method, and the application of cerium oxide-copper oxide composite catalytic materials doped with rubidium in the selective oxidation of aniline synthesis oxidized azo compound, belongs to the field of catalysis. BACKGROUND

[0002] Azo compounds, as a kind of important organic compounds in modern industry, have a wide application in the fields of dyes, food additives, drugs, optoelectronic materials, etc. The traditional synthesis method of azo compounds needs to use diazonium salt, a large amount of hydrochloric acid, and produces a large amount of by-products. In view of the above problems, the use of catalyst system to directly catalyze the oxidation of aniline to synthesize azo compounds is a new synthesis method. However, the existing catalytic materials have problems such as high cost of catalyst, use of toxic oxidizing agent, harsh reaction conditions, and poor controllability of target product. The existing catalytic materials are difficult to achieve high conversion rate and selectivity at the same time, therefore, it is necessary to develop a low-cost catalyst with high conversion rate and high selectivity to realize the efficient synthesis of azo compounds.

[0003] The existing ceria-based nanocatalyst has reversible Ce 3+ / Ce 4+ Oxidation-reduction pair, controllable surface oxygen vacancy and good surface acid-base property, etc. are widely used, among which, the ceria-based nanocatalyst loaded with copper has excellent catalytic performance due to the interaction between copper nanoparticles and the carrier. In the synthesis of azo compounds, the adsorption of aniline on the surface of the CeO2 carrier makes the reaction conversion rate good, and H2O2 is decomposed into specific oxygen species on the surface of copper oxide, which can target recognition to synthesize azo benzene. However, the Cu / CeO2 catalyst is difficult to achieve high conversion rate and selectivity at the same time in the synthesis of azo compounds, and the leaching of Cu ions in the reaction leads to rapid attenuation of catalytic activity, which seriously limits its large-scale application. SUMMARY

[0004] In view of the defects and deficiencies of the above-mentioned technology, the first object of the present application is to provide a cerium oxide-copper oxide composite catalytic material doped with rubidium. This catalytic material is based on the doping modification of trace rubidium on cerium oxide-copper oxide composite catalytic material, which can effectively control the surface properties of the catalytic material, enhance its catalytic performance and stability, and endow it with the advantages of high selectivity, good conversion rate, stability and long service life.

[0005] The second object of the present application is to provide a preparation method of cerium oxide-copper oxide composite catalytic material doped with rubidium. This method is simple in operation, short in time consumption and low in cost.

[0006] A third object of the present application is to provide an application of the rubidium-doped cerium oxide-copper oxide composite catalytic material in a reaction of catalytic oxidation of aniline to synthesize azoxocompounds, using H2O2 as an oxidant, to achieve targeted recognition of azoxocompounds and high-efficiency catalysis under low-temperature and normal-pressure conditions, and the catalytic material has good stability and long service life.

[0007] To achieve the above technical objects, the present application provides a rubidium-doped cerium oxide-copper oxide composite catalytic material, which is composed of rubidium doping on the surface of a copper-cerium composite material; the copper-cerium composite material is composed of copper oxide nanoparticles grown on cerium oxide nanorods.

[0008] The rubidium-doped cerium oxide-copper oxide composite catalytic material provided by the present application is mainly composed of copper-cerium composite catalytic material with copper oxide nanoparticles supported on cerium oxide nanorods, which is modified by rubidium doping. The cerium oxide nanorods in the copper-cerium composite catalytic material have good oxygen storage capacity, and the copper oxide nanoparticles have the function of targeted recognition of azoxocompounds, so that the combination of the two exhibits high catalytic activity and high catalytic selectivity for aniline oxidation. In particular, after the copper-cerium composite catalytic material is modified by rubidium ion doping, the electron transfer between the cerium oxide nanorods and the copper oxide nanoparticles in the catalytic reaction process can be effectively controlled, the interaction between the copper oxide nanoparticles and the cerium oxide nanorod carrier is enhanced, the concentration of active sites on the surface of the catalytic material is increased, and the catalytic activity and stability are effectively improved.

[0009] As a preferred scheme, the mass of the copper oxide nanoparticles in the copper-cerium composite material is 7-9% of the mass of the cerium oxide nanorods. Too low loading of copper oxide will result in a small number of active sites on the surface of the catalyst and poor catalytic performance. Too high loading of copper oxide will affect its dispersibility on the surface of the catalyst and also cause agglomeration and reduce the number of active sites on the surface.

[0010] As a preferred scheme, the doping amount of rubidium in the copper-cerium composite material is 0.1-0.3wt.%. Rubidium mainly plays a role in promoting the electron transfer performance of the catalyst surface, and a low doping amount has a limited effect on promoting the catalytic performance. A high doping amount will reduce the specific surface area of the catalyst and reduce the catalytic performance.

[0011] The present application also provides a preparation method of the rubidium-doped cerium oxide-copper oxide composite catalytic material, which comprises the following steps: adding a cerium salt solution dropwise into an alkali solution to form a suspension A, subjecting the suspension A to a hydrothermal reaction to obtain a suspension B; sequentially mixing, solid-liquid separation, drying and calcining I of the suspension B and a copper salt to obtain a copper-cerium composite material; and immersing the copper-cerium composite material in a rubidium salt solution and then calcining II to obtain the rubidium-doped cerium oxide-copper oxide composite catalytic material.

[0012] As a preferred embodiment, the alkaline solution is a sodium hydroxide solution with a concentration of 15–25 wt.%. The main function of the alkaline solution is to react completely with the cerium salt solution to form cerium hydroxide precipitate, and to control the pH of the solution to ensure the growth of morphologically stable cerium oxide nanorod supports in the subsequent hydrothermal reaction. Excessive sodium hydroxide concentration will affect the morphology of cerium oxide, thereby affecting catalytic activity. Insufficient concentration will result in incomplete reaction of the cerium salt solution, leading to waste.

[0013] As a preferred embodiment, the concentration of the cerium salt solution is 10–15 wt.%.

[0014] As a preferred embodiment, the cerium salt includes cerium chloride and / or cerium chloride hydrate. Theoretically, any cerium salt with good water solubility meets the requirements, with cerium chloride being the most common.

[0015] As a preferred embodiment, the hydrothermal reaction conditions are: temperature 100–120°C and time 20–24 h. The reaction temperature and reaction time mainly affect the grain size and crystal morphology of cerium oxide. Under the preferred temperature and time conditions, it can be ensured that cerium oxide forms a nanorod-like morphology.

[0016] As a preferred embodiment, the mass ratio of the copper salt to the cerium salt is (0.13 to 0.21):1.

[0017] As a preferred embodiment, the copper salt comprises copper nitrate and / or copper nitrate hydrate. Theoretically, copper salts with good water solubility meet the requirements, with copper nitrate being the most common.

[0018] As a preferred embodiment, the calcination conditions are: temperature 400–450°C, time 4–8 hours. Temperature is the main factor affecting the performance of the catalytic material, while the time is adjusted appropriately according to the temperature. Excessively high calcination temperatures can lead to sintering of the catalytic material, causing a sharp decrease in surface area. Conversely, excessively low calcination temperatures can result in residual volatile components and fewer surface pores on the catalyst. Both excessively high and excessively low calcination temperatures lead to a decrease in catalytic activity.

[0019] As a preferred embodiment, the concentration of the rubidium salt solution is 0.1–0.3 M;

[0020] As a preferred embodiment, the rubidium salt includes at least one of rubidium nitrate, rubidium chloride, and rubidium sulfate. Theoretically, any rubidium salt with good water solubility meets the requirements. Rubidium nitrate is a common example.

[0021] As a preferred embodiment, the solid-liquid ratio of the copper-cerium composite material in the rubidium salt solution is 500 mg to 1000 mg / L. An excessively high solid-liquid ratio leads to poor dispersibility of the copper-cerium composite material in the impregnation solution, resulting in uneven distribution of rubidium ions after doping. Conversely, an excessively low solid-liquid ratio results in excessively high rubidium ion doping on the copper-cerium composite material, leading to a high rubidium salt concentration in the impregnation solution after impregnation equilibrium, thus causing waste.

[0022] As a preferred embodiment, the impregnation conditions are: time of 60–240 min, rotation speed of 300–500 rpm, and temperature of 25–50 °C. The doped rubidium ions, acting as an electron modifier, can regulate electron transfer on the surface of the catalytic material through interaction with copper oxide on the copper-cerium composite material, thereby increasing the catalytic activity of the copper-cerium composite material. When the molar concentration of the rubidium salt impregnation solution is low and the impregnation time is short, there are fewer rubidium ions doped on the support, resulting in weak electron transfer regulation and low catalytic activity. Excessively high molar concentrations of the rubidium salt impregnation solution and excessively long impregnation times lead to higher rubidium doping levels, causing support particle agglomeration and reduced porosity, resulting in decreased catalytic activity.

[0023] As a preferred embodiment, the calcination conditions for step II are: a temperature of 400–450°C and a time of 4–8 hours. If the calcination temperature for step II is too low, the rubidium ions on the catalyst surface will have poor stability and uneven distribution, ultimately resulting in a catalyst with low catalytic activity. If the calcination temperature for step II is too high, it will lead to problems such as catalyst sintering, grain growth, and poor dispersion of nanoparticles, also resulting in a catalyst with low catalytic activity.

[0024] The present invention provides a method for preparing a rubidium-doped cerium oxide-copper oxide composite catalytic material, comprising the following steps:

[0025] 1) Add sodium hydroxide to water and stir until dissolved. Then add cerium salt solution and stir to obtain white suspension A.

[0026] 2) Place suspension A in a polytetrafluoroethylene-lined reactor and carry out a hydrothermal reaction using an oven as a heat source; after the hydrothermal reaction is completed, add copper salt to suspension A and stir to dissolve to obtain green suspension B;

[0027] 3) After filtering, washing and drying the suspension B, the resulting powder is calcined in air to obtain the copper-cerium composite material.

[0028] 4) The copper-cerium composite material is added to the rubidium salt solution to form a suspension. After stirring, the suspension is filtered, washed and dried. The resulting powder is calcined in air to obtain the rubidium-doped nano-cerium oxide supported copper catalyst.

[0029] This invention also provides an application of a rubidium-doped cerium oxide-copper oxide composite catalytic material, which is used to catalyze the oxidation of aniline to synthesize azo compounds. It can achieve efficient conversion of aniline into the product under low temperature and ambient pressure conditions, and highly selective synthesis of azo compounds.

[0030] As a preferred method, the conditions for the oxidation of aniline to synthesize azo compounds are: temperature 25–100℃, time 4–24 h, hydrogen peroxide solution to aniline volume ratio of (20–25):1, and catalyst to aniline mass to volume ratio of (500–1000) mg:1 mL. The hydrogen peroxide solution is 30% industrial hydrogen peroxide.

[0031] The rubidium-doped cerium oxide-copper oxide composite catalytic material provided by this invention, in the reaction of aniline-catalyzed synthesis of azo compounds, proceeds as follows: First, reaction ① involves hydrogen peroxide being adsorbed onto copper ions on the catalyst surface and reacting to generate superoxide radicals; then, reaction ② involves aniline reacting with superoxide radicals to generate the intermediate phenylhydroxylamine, which is further oxidized to the intermediate nitrosbenzene; then, reaction ③ involves phenylhydroxylamine reacting with nitrosbenzene to generate the target product azobenzene; furthermore, reaction ④ involves a small amount of aniline reacting with phenylhydroxylamine to generate the byproduct azobenzene; and reaction ⑤ involves a small amount of unreacted intermediate nitrosbenzene being oxidized to nitrobenzene. The rubidium doping in the catalytic material can improve the reaction rate of copper ions with hydrogen peroxide in reaction ① by regulating electron transfer, accelerating the conversion of aniline to the intermediates phenylhydroxylamine and nitrosbenzene, reducing the occurrence of side reactions, thereby simultaneously improving conversion rate and selectivity, demonstrating the substrate specificity of the rubidium-doped cerium oxide-copper oxide composite catalytic material.

[0032] The rubidium-doped cerium oxide-copper oxide composite catalyst of the present invention (hereinafter referred to as Rb-Cu / CeO2) is used for the catalytic oxidation of aniline: aniline is used as the reactant, toluene as the solvent, and hydrogen peroxide solution as the oxidant, under the reaction conditions of a stirring speed of 300-500 rpm, a reaction temperature of 25-100℃, and a reaction time of 4-24 h to synthesize azobenzene. The amount of toluene solvent used is 2-3 ml, the volume ratio of hydrogen peroxide solution to aniline is (20-25):1, and the mass-to-volume ratio of catalyst to aniline is (500-1000) mg:1 ml.

[0033] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0034] 1) The preparation method of Rb-Cu / CeO2 provided by this invention is simple, low-cost, and environmentally friendly and controllable, and can be industrialized for large-scale production.

[0035] 2) The Rb-Cu / CeO2 provided by this invention improves the activity of the catalyst by using rubidium ions as an electronic modifier to participate in and accelerate the electron transfer process of the reaction between copper ions and aniline, thus achieving high specificity, high conversion rate and long service life.

[0036] 3) The Rb-Cu / CeO2 provided by this invention is applied to the reaction of catalytic oxidation of aniline to synthesize azobenzene. It achieves high-efficiency catalysis with high conversion rate and high selectivity of target product under normal pressure and low temperature conditions. The reaction process has the characteristics of low cost, controllability and environmental friendliness. Attached Figure Description

[0037] Figure 1 The process flow diagram for preparing the rubidium-doped cerium oxide-copper oxide composite catalytic material provided by the present invention is shown.

[0038] Figure 2 The XRD diffraction patterns of the cerium oxide-copper oxide composite catalyst (8% Cu / CeO2) and the rubidium-doped cerium oxide-copper oxide composite catalyst (0.2% Rb-8% Cu / CeO2) in Example 1 are shown below. Figure 2 It can be seen that the main diffraction peaks correspond to the crystal plane of CeO2, while there are no diffraction peaks of CuO. This indicates that CuO is highly dispersed on the catalyst surface and its content is low. Rubidium doping did not cause the original diffraction peaks to disappear or new diffraction peaks to be generated. This indicates that rubidium oxide exists in an amorphous state and its content is extremely low.

[0039] Figure 3 The cerium oxide-copper oxide composite catalyst (8% Cu / CeO2) in Example 1 Figure 3 (a) and Figure 3 (b) and rubidium-doped cerium oxide-copper oxide composite catalyst (0.2% Rb-8% Cu / CeO2) Figure 3 (c) and Figure 3 (d) SEM comparison image; from Figure 3 (a) and Figure 3 (b) shows that cerium oxide has a nanorod-like structure, while copper oxide has a nanoparticle morphology. The copper oxide nanoparticles are supported on the cerium oxide nanorods. Figure 3 (c) and Figure 3 As shown in (d), the structure of the catalytic material did not change significantly before and after rubidium doping, but the dispersion of the catalyst was improved after rubidium doping. Detailed Implementation

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0043] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] Example 1

[0046] 1.49 g of CeCl3·7H2O was dissolved in 10 ml of deionized water to obtain a CeCl3 solution. 16.8 g of NaOH was dissolved in 70 ml of deionized water and stirred at room temperature for 10 min until the NaOH was completely dissolved to obtain a NaOH solution. The CeCl3 solution was then added dropwise to the NaOH solution while stirring continuously for 30 min to obtain a white suspension A. Suspension A was then transferred to a 100 ml polytetrafluoroethylene-lined reactor and subjected to hydrothermal reaction at 100 °C for 24 h using an oven as the heat source. After the hydrothermal reaction was completed, the reactor was cooled to room temperature, the solution was poured out, and 0.208 g of Cu(NO3) was added. 2.The mixture was stirred for 18 hours with 3H₂O, then filtered and washed several times with deionized water and anhydrous ethanol to obtain the filter residue, which was then dried at 60°C for 12 hours. Finally, the dried powder was calcined at 400°C for 2 hours to obtain the Cu / CeO₂ catalyst. Then, 500 mg of the Cu / CeO₂ catalyst was added to a 0.1–0.3 M rubidium nitrate solution and stirred at 400 rpm for 120 minutes. After impregnation, the filter residue was dried at 60°C for 12 hours, and the dried powder was calcined at 400°C for 2 hours to obtain Rb-Cu / CeO₂ catalysts with different rubidium contents. The copper loading in the Rb-Cu / CeO₂ catalyst was 8 wt%, and the rubidium content was 0.1–0.3 wt%. The obtained catalyst was used for a catalytic reaction. First, 0.1 ml of aniline was dissolved in 2 ml of toluene, then 2 ml of hydrogen peroxide solution and 50 mg of catalyst were added. The mixture was then added to a 50 ml round-bottom flask and reacted at a stirring speed of 300 rpm. The reaction time was 12 h, and the reaction temperature was 100 °C. The products obtained were azobenzene oxide (AOB), azobenzene (AB), nitrosobenzene (NSB), and nitrobenzene (NOB). The catalytic reaction results are shown in Table 1.

[0047] Table 1 Comparison of catalytic performance between Cu / CeO2 and Rb-Cu / CeO2 catalysts

[0048]

[0049] As shown in Table 1, the catalytic efficiency and azobenzene oxide yield of the Rb-Cu / CeO2 catalyst in the above-mentioned catalytic oxidation of aniline are higher than those of the Cu / CeO2 catalyst under the same reaction conditions. This confirms the promoting effect of rubidium doping on the catalytic efficiency and azobenzene oxide yield. 0.2 wt% is the optimal rubidium doping amount. Too low a rubidium doping amount will result in limited improvement in catalytic activity, while too high a rubidium doping amount will lead to increased by-product yield and decreased azobenzene oxide yield, thereby reducing the selectivity of the catalyst.

[0050] Example 2

[0051] Compared with Example 1, other conditions remained unchanged, except that the catalyst used was 0.2% Rb-8% Cu / CeO2, and the secondary calcination temperature was changed to 300–500 °C. The prepared catalyst was denoted as 0.2% Rb-8% Cu / CeO2-T (T = 300, 350, 400, 450, 500). The catalytic reaction temperature was 100 °C, and the reaction time was 12 h. The experimental results are shown in Table 2.

[0052] Table 2. Effect of different secondary calcination temperatures on the catalytic performance of 0.2% Rb-8% Cu / CeO2 catalyst

[0053]

[0054] As shown in Table 2, between 300 and 400℃, the catalytic efficiency and AOB yield continuously increase with increasing calcination temperature. Between 400 and 500℃, both catalytic efficiency and AOB yield decrease slightly with increasing calcination temperature. Generally, calcination helps remove volatile substances and gives the catalyst a certain pore size and surface area, which is a key step in activating the catalyst. Lower calcination temperatures will not achieve complete catalyst activation and will not yield optimal catalytic performance. Excessively high calcination temperatures will cause sintering, thus reducing catalytic performance. To ensure complete catalyst activation and achieve optimal catalytic performance, 400℃ is the optimal secondary calcination temperature.

[0055] Example 3

[0056] Compared with Example 1, other conditions remained unchanged, the catalyst used was 0.2% Rb-8% Cu / CeO2, the reaction temperature was 25-100℃, and the reaction time was 4h. The experimental results are shown in Table 3.

[0057] Table 3. Effect of different reaction temperatures on the catalytic performance of the 0.2% Rb-8% Cu / CeO2 catalyst.

[0058]

[0059] As shown in Table 3, at 25℃, a significant amount of aniline did not participate in the reaction, and the intermediate nitrosbenzene was the main product of aniline oxidation. When the temperature increased to 50℃, the catalytic rate significantly improved, and the yield of nitrosbenzene decreased while the yield of azobenzene oxide increased, indicating that higher temperatures favored the conversion of the intermediate nitrosbenzene to azobenzene oxide. Between 75 and 100℃, the yield of azobenzene oxide increased rapidly, indicating that higher temperatures provided better catalyst recognition for the synthesis of azobenzene oxide, with the highest yield observed at 100℃.

[0060] Example 4

[0061] Compared with Example 1, other conditions remained unchanged, except that the catalyst used was 0.2% Rb-8% Cu / CeO2, and the reaction time was changed to 4–24 h. The experimental results are shown in Table 4.

[0062] Table 4. Effects of different reaction times on the catalytic performance of the 0.2% Rb-8% Cu / CeO2 catalyst.

[0063]

[0064] According to the experimental results in Table 4, the catalytic rate and the yield of azobenzene oxide initially increased and then decreased with increasing reaction time. The catalytic rate and yield of azobenzene oxide were relatively good at 12 h. Although the yield of azobenzene oxide increased at 18 h, the catalytic rate decreased. When the reaction time was short, the aniline involved in the reaction was first oxidized to intermediates such as nitrosamine, and some aniline did not participate in the reaction, thus the catalytic rate and the yield of azobenzene oxide were not high. When the reaction time reached 24 h, the oxidant H2O2 was almost completely used up, and the reaction rate for the formation of azobenzene oxide decreased. In addition, some azobenzene oxide was reduced to aniline, thus the catalytic rate and the yield of azobenzene oxide decreased.

[0065] Example 5

[0066] Compared with Example 1, other conditions remained unchanged, except that the catalyst used was 0.2% Rb-8% Cu / CeO2, and the amount of catalyst was changed to 25-100 mg.

[0067] Table 5. Effect of different catalyst dosages on the catalytic performance of the 0.2% Rb-8% Cu / CeO2 catalyst.

[0068]

[0069] The results show that the catalytic effect is limited at a catalyst dosage of 20 mg, but significantly improves with increasing catalyst dosage. The highest catalytic efficiency is achieved at 50 mg catalyst dosage. As the dosage increases to 75 mg, the catalytic efficiency decreases, but the yield of azobenzene oxide does not increase significantly. At 100 mg catalyst dosage, catalyst particle agglomeration is evident, reducing the number of active sites involved in the reaction, and both the catalytic efficiency and yield decrease. Therefore, catalyst dosages of 75 mg and 100 mg do not significantly improve the catalytic efficiency and azobenzene oxide yield, but instead increase costs. Thus, the optimal catalyst dosage is 50 mg.

[0070] Example 6

[0071] Compared with Example 1, other conditions remained unchanged, except that the catalyst used was 0.2% Rb-8% Cu / CeO2, and the amount of H2O2 was changed to 0.5-3 ml.

[0072] Table 6. Effect of different H2O2 dosages on the catalytic performance of the 0.2% Rb-8% Cu / CeO2 catalyst.

[0073]

[0074]

[0075] According to the experimental results, the catalytic rate was less than 50% with 0.5 ml of H2O2 because the number of active oxygen species participating in the reaction was too small, resulting in incomplete oxidation. As the amount of H2O2 increased, the number of active oxygen species participating in the reaction increased, leading to a significant increase in the catalytic rate, but only a slight increase in the yield of azobenzene oxide. The optimal catalytic rate and azobenzene oxide yield were achieved with 2 ml of H2O2. With 3 ml of H2O2, the catalytic rate and yield decreased due to excessive oxidation of aniline by excess active oxygen species.

Claims

1. A rubidium-doped cerium oxide-copper oxide composite catalytic material, characterized in that: It is composed of rubidium doping on the surface of a copper-cerium composite material; the copper-cerium composite material is composed of copper oxide nanoparticles grown on cerium oxide nanorods; The mass of copper oxide nanoparticles in the copper-cerium composite material is 7-9% of the mass of cerium oxide nanorods; The rubidium doping content in the copper-cerium composite material is 0.1~0.3 wt.%.

2. The preparation method of the rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 1, characterized in that: A cerium salt solution is added dropwise to an alkaline solution to form a suspension A. The suspension A undergoes a hydrothermal reaction to obtain a suspension B. The suspension B and a copper salt are then subjected to mixing, solid-liquid separation, drying, and calcination I in sequence to obtain a copper-cerium composite material. The copper-cerium composite material is obtained by impregnating it in a rubidium salt solution and then calcining it.

3. The method for preparing a rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 2, characterized in that: The alkaline solution is a sodium hydroxide solution with a concentration of 15~25 wt.%. The concentration of the cerium salt solution is 10~15 wt.%; The cerium salt includes cerium chloride and / or cerium chloride hydrate; The conditions for the hydrothermal reaction are: temperature 100~120℃, time 20~24h.

4. The method for preparing a rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 2, characterized in that: The mass ratio of the copper salt to the cerium salt is (0.13~0.21):1; The copper salt includes copper nitrate and / or copper nitrate hydrate.

5. The method for preparing a rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 2 or 4, characterized in that: The conditions for calcination I are: temperature 400~450℃, time 4~8h.

6. The method for preparing a rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 2, characterized in that: The concentration of the rubidium salt solution is 0.1~0.3M; The rubidium salt includes at least one of rubidium nitrate, rubidium chloride, and rubidium sulfate.

7. The method for preparing a rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 2 or 6, characterized in that: The impregnation conditions are: time of 60~240min, rotation speed of 300~500rpm, and temperature of 25~50℃; The conditions for calcination II are: temperature 400~450℃, time 4~8h.

8. The application of the rubidium-doped cerium oxide-copper oxide composite catalytic material according to claim 1, characterized in that: It is used to catalyze the oxidation of aniline to synthesize azo compounds.

9. The application according to claim 8, characterized in that: The conditions for the synthesis of azo compounds by aniline oxidation are: temperature 25~100℃, time 4~24h, volume ratio of hydrogen peroxide solution to aniline (20~25):1, and mass-volume ratio of catalyst to aniline (500~1000) mg:1 mL.

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