A rubidium-doped nano cerium oxide supported gold catalyst, a preparation method and application thereof

Abstract

The application discloses a rubidium-doped nano cerium oxide supported gold catalyst and a preparation method and application thereof, and the catalyst is composed of nano gold supported on rubidium-doped cerium oxide nanoparticles. The catalyst is prepared by the following steps: mixing solution A containing dissolved glucose and a gold source with solution B containing dissolved urea and a cerium salt, then performing hydrothermal reaction to obtain a precursor; then performing calcination I on the precursor to obtain nano cerium oxide supported gold particles; and finally performing calcination II on the nano cerium oxide supported gold particles after the nano cerium oxide supported gold particles are immersed in a rubidium salt solution. The preparation method has the advantages of simple synthesis operation, low cost and easy industrial production. The material is applied to the reaction of catalytic synthesis of azo compounds from aniline, and has the advantages of high catalytic activity, high efficiency and environmental friendliness.

Description

Technical Field

[0001] This invention relates to a gold catalyst supported on cerium oxide nanoparticles and its preparation method, specifically to a rubidium-doped gold catalyst supported on cerium oxide nanoparticles and its preparation method. This invention also relates to the application of a rubidium-doped gold catalyst supported on cerium oxide nanoparticles in the catalytic synthesis of azo compounds from aniline, belonging to the field of catalytic environmental protection technology. Background Technology

[0002] Azo compounds are a class of very important organic compounds with significant applications in chemical engineering, optoelectronic materials, energetic materials, organic synthesis, medicinal chemistry, and synthetic dyes. However, existing methods for preparing azo compounds via catalytic reactions suffer from problems such as harsh reaction conditions, numerous byproducts, and high costs. Therefore, developing novel metal catalysts with high conversion rates and high specificity is crucial for the efficient synthesis of azo compounds. Currently, the catalytic conversion rates of existing patents are around 90%, while the yields of azobenzene oxide are between 80% and 90%, making it difficult to simultaneously achieve high conversion rates and specificity. For example, the MOFs-supported Co-C magnetic catalyst prepared by Chinese patent CN109928898A and the cuprous chloride composite catalyst prepared by Chinese patent CN 107353233A can both effectively improve the catalytic efficiency of synthesizing azobenzene oxide from aromatic hydrocarbon compounds. Although the highest catalytic conversion rates are both above 90%, the highest yields of azobenzene oxide are only around 80%, indicating poor target recognition in the catalytic reaction process and resulting in low raw material utilization. Therefore, developing highly efficient catalysts that simultaneously possess high specificity and conversion rate remains a challenge.

[0003] Supported noble metal nanocatalysts are formed by loading noble metal active components onto specific supports such as metal oxides, molecular sieves, and metal-organic frameworks (MOFs). Due to their excellent catalytic activity, easy separation from the reaction substrate, high reaction specificity, and recyclability, they are widely used in the synthesis of azo compounds. Among them, Au catalysts supported on metal oxides exhibit high activity in the synthesis of azo compounds, demonstrating excellent catalytic performance under mild conditions. Au-supported metal oxides can target and recognize the catalytic reaction of aniline as a substrate to produce phenylhydroxylamine and nitrosamine, as well as the catalytic reaction of phenylhydroxylamine and nitrosamine as substrates to synthesize azobenzene oxide, while also exhibiting catalytic side reactions of aniline and phenylhydroxylamine to produce azobenzene. However, small-sized Au-supported metal oxide catalysts are often unstable, easily agglomerating or clustering under catalytic reaction conditions, losing their original unique nanoscale properties and rapidly declining catalytic activity, severely hindering their practical application. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the first objective of this invention is to provide a rubidium-doped cerium oxide nanoparticle-supported gold catalyst that simultaneously possesses high specificity, good conversion rate, high stability, and long service life. This catalyst utilizes the doping and substitution of trace amounts of rubidium in the Au@CeO2 lattice to regulate the surface properties of the Au@CeO2 catalyst and enhance the interaction between the gold nanoparticles and the support, effectively stabilizing the uniform dispersion of the gold nanoparticles on the support surface.

[0005] The second objective of this invention is to provide a method for preparing a rubidium-doped cerium oxide nano-supported gold catalyst, which is simple in process, low in cost, and easy to industrialize.

[0006] The third objective of this invention is to provide an application of a rubidium-doped cerium oxide nano-supported gold catalyst, which is used in the catalytic synthesis of azo compounds from aniline to achieve targeted identification of azo compounds and their byproducts and high-yield, high-efficiency catalysis under low-temperature conditions.

[0007] To achieve the above-mentioned technical objectives, the present invention provides a rubidium-doped cerium oxide nanoparticle-supported gold catalyst, which is composed of gold nanoparticles supported on rubidium-doped cerium oxide nanoparticles.

[0008] The rubidium-doped cerium oxide nanoparticles supported on gold catalyst provided by this invention use highly stable and non-agglomerated cerium oxide (CeO2) as a support to support a composite catalyst material with high catalytic efficiency Au. By doping and substituting trace amounts of Rb in the Au@CeO2 lattice, the low ionization energy of the free electrons released by Rb can rapidly replenish electrons to Au ions, restoring their electroneutrality and maintaining catalytic activity. This can weaken the side reaction catalytic ability with aniline and phenylhydroxylamine as substrates, regulate the surface properties of the Au@CeO2 catalyst, and enhance the interaction between the gold nanoparticles and the support, effectively stabilizing the uniform dispersion of the gold nanoparticles on the support surface.

[0009] As a preferred embodiment, the loading amount of gold nanoparticles on rubidium-doped cerium oxide nanoparticles is 1–3 wt.%, and the rubidium doping amount in the rubidium-doped cerium oxide nanoparticles is 0.01–0.02 wt.%.

[0010] This invention also provides a method for preparing a rubidium-doped cerium oxide nanoparticle-supported gold catalyst. The method involves mixing a solution A containing glucose and a gold source with a solution B containing urea and a cerium salt, followed by a hydrothermal reaction to obtain a precursor. The precursor is then calcined (I) to obtain cerium oxide nanoparticle-supported gold particles. The cerium oxide nanoparticle-supported gold particles are then immersed in a rubidium salt solution and calcined (II) to obtain the final product.

[0011] As a preferred embodiment, the glucose concentration in solution A is 5–8 wt.%, and the mass ratio of glucose to gold source is (200–300):1. The main function of glucose is to reduce trivalent gold ions to nano-gold particles, which are then uniformly dispersed. During the calcination stage, glucose is removed by combustion, and trace amounts of glucose simultaneously form gold particles supported on carbon nanospheres. Both excessively high and low glucose concentrations will reduce the activity of the catalyst gold particles.

[0012] As a preferred embodiment, the cerium salt comprises cerium chloride and / or cerium chloride hydrate; the concentration of urea in solution B is 5–8 wt.%; and the mass ratio of urea to cerium salt in solution B is (0.1–0.5):1. Urea releases OH-. - Ions provide an alkaline environment, and the deprotonation of functional groups such as carboxyl groups can enhance the resistance to Ce. 3+ Due to electrostatic adsorption, free Ce exists in urea solution. 3+ Less. Both excessively high and low urea concentrations will reduce the performance of the CeO2 catalyst.

[0013] As a preferred embodiment, the gold source is chloroauric acid and its hydrate.

[0014] As a preferred embodiment, the hydrothermal reaction conditions are: temperature of 150-200℃ and time of 12-24h, with the hydrothermal temperature determining the duration of the hydrothermal reaction.

[0015] As a preferred embodiment, the calcination conditions are: temperature 550–650℃, time 4–10 h. The calcination temperature determines the calcination reaction time. Furthermore, if the calcination temperature is too high, the cerium oxide support crystals will collapse severely; if the calcination temperature is too low, the organic matter and metal oxides will not decompose sufficiently, and the catalyst activity will decrease.

[0016] As a preferred embodiment, the rubidium salt includes at least one of rubidium nitrate, rubidium chloride, and rubidium sulfate. The molar concentration of rubidium is 0.1–0.5 M. Alkali metal doping can increase the activity of the Au / CeO2 catalyst. During catalysis, metallic gold loses electrons to become gold ions. By adding Rb, the gold ions in the catalyst can more easily accept low-ionization-energy alkali metal electrons, becoming electrically neutral gold and regaining excellent catalytic activity. In this way, the electronic defects of the gold metal are regularly compensated by Rb, enhancing catalytic activity and continuing in a cyclical manner. If the molar concentration of rubidium is too low, the doping amount is insufficient, resulting in low catalytic activity. Conversely, if the molar concentration of rubidium is too high, the doping amount will be excessive, leading to easy ion aggregation on the catalyst surface and a decrease in the catalyst's specific surface area. Ultimately, this inhibits the compensation effect of Rb on the electronic defects of the gold metal, thus reducing the yield of product A. As a preferred embodiment, the mass ratio of the cerium oxide nanoparticles loaded with gold to the rubidium salt is (100-200):1.

[0017] As a preferred approach, the concentration of gold nanoparticles supported on cerium oxide in rubidium salt is 200–500 mg / L. Excessive catalyst concentration leads to agglomeration and poor doping modification. Conversely, excessively low catalyst suspension concentration results in low yield per modification cycle and increased doping modification costs.

[0018] As a preferred embodiment, the impregnation conditions are: time of 30–60 min, rotation speed of 100–400 rpm, and temperature of 25–90 °C. Impregnation allows rubidium to be fully incorporated into the structure of the nano-cerium oxide-supported gold catalyst.

[0019] As a preferred embodiment, the conditions for calcination II are: a temperature of 550–650°C and a time of 4–10 h. If the calcination II temperature is too low, the removal of volatile components will be incomplete, the increase in specific surface area will be small, and the resulting catalyst will have low activity. If the calcination II temperature is too high, structural changes such as catalyst sintering, a sharp decrease in specific surface area, and increased grain size will occur, which will also reduce catalytic activity. This invention provides a method for preparing a rubidium-doped cerium oxide nano-supported gold catalyst, comprising the following steps:

[0020] 1) Dissolve glucose in an aqueous solution, then add gold source to it, stir and dissolve to obtain a clear yellow solution A;

[0021] 2) Dissolve urea in water, then add cerium salt to it, stir and dissolve to obtain a clear solution B;

[0022] 3) Add solution B to solution A under stirring, and disperse evenly to obtain a clear yellow solution C;

[0023] 4) Place solution C in a polytetrafluoroethylene high-temperature reactor for hydrothermal reaction. After the hydrothermal reaction is completed, wash, filter and dry.

[0024] 5) The dried powder is calcined at high temperature under air conditions to obtain nano-cerium oxide supported gold catalyst;

[0025] 6) Disperse the nano-cerium oxide-supported gold catalyst in a rubidium-containing solution to form a suspension. After stirring, impregnation and modification, wash, filter and dry. The resulting powder is calcined at high temperature under air conditions to obtain the rubidium-doped nano-cerium oxide-supported gold catalyst.

[0026] The present invention also provides an application of rubidium-doped cerium oxide nanoparticles supported on gold catalysts, which are used as catalysts for the synthesis of azo compounds from aniline. This enables targeted identification of azo compounds and their byproducts and exhibits high catalytic activity at low temperatures.

[0027] The rubidium-doped cerium oxide nano-supported gold catalyst provided by this invention, in the catalytic synthesis of azo compounds from aniline, proceeds as follows: First, reaction ① involves the formation of phenylhydroxylamine and nitrosylbenzene from aniline; then, reaction ② involves the condensation of phenylhydroxylamine and nitrosylbenzene on the catalyst surface to form azobenzene as the target product; furthermore, reaction ③ involves the reaction of some unreacted aniline with phenylhydroxylamine to form azobenzene as a byproduct. Rb-Au / CeO2 can increase the reaction rate of aniline to phenylhydroxylamine and nitrosylbenzene in reaction ①, reduce the amount of residual unreacted aniline in the catalytic system, and thus reduce the occurrence of side reaction ③. This weakens the catalytic ability of side reactions using aniline and phenylhydroxylamine as substrates, demonstrating the specificity of this catalyst for its catalytic substrate.

[0028] As a preferred embodiment, the catalytic rate and selectivity of Au / CeO2 and Rb-Au / CeO2 nanoparticles obtained in steps 5) and 6) for the synthesis of azobenzene from aniline under different conditions were analyzed. The catalytic reaction involved adding the synthesized catalyst to toluene as a solvent, along with hydrogen peroxide, to catalyze the synthesis of azobenzene from aniline. The aniline volume concentration in the toluene solvent was 2–5%, the volume ratio of analytical grade hydrogen peroxide to aniline was (10–20):1, and the catalyst volume ratio to aniline mass was (200–750) mg:1 mL. The catalytic reaction was carried out at a stirring speed of 200–400 rpm for 4–24 h and at a temperature of 50–100 °C.

[0029] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0030] 1) The rubidium-doped nano-cerium oxide supported gold catalyst provided by the present invention can rapidly replenish the electrons of the active component Au ions by ionizing the Rb in the rubidium co-catalyst to restore its electroneutrality, thus maintaining the activity of the catalyst. It has high specificity, good conversion rate, high stability and long service life.

[0031] 2) The method for preparing rubidium-doped nano-cerium oxide supported gold catalyst provided by the present invention is simple, low-cost, and easy to industrialize.

[0032] 3) The rubidium-doped cerium oxide nano-supported gold catalyst provided by this invention is applied to the reaction of aniline catalytic synthesis of azo compounds, achieving high yield and high efficiency catalysis under low temperature conditions, while improving the selectivity of azo compound synthesis in the product, greatly reducing catalytic cost, and has the characteristics of low cost, high efficiency and environmental friendliness. Attached Figure Description

[0033] Figure 1 This is a flowchart of the preparation method of the rubidium-doped cerium oxide nano-supported gold catalyst of the present invention.

[0034] Figure 2 The images show a comparison of the XRD patterns of the gold catalyst supported on cerium oxide nanoparticles and the rubidium-doped gold catalyst supported on cerium oxide nanoparticles in Example 1. Figure 2 It can be seen that there is no obvious formation or disappearance of diffraction peaks before and after doping, indicating that trace amounts of rubidium are only doped and substituted in the Au@CeO2 lattice, thereby regulating the surface properties of the catalyst.

[0035] Figure 3 The gold catalyst supported on nano-cerium oxide in Example 1 ( Figure 3 (a) and Figure 3 (c) and rubidium-doped cerium oxide nano-supported gold catalyst ( Figure 3 (b) and Figure 3 (d) SEM-EDS comparison image. There was no obvious morphological change before and after rubidium doping, but EDS could detect trace amounts of rubidium in the Rb-Au@CeO2 material, further verifying that rubidium doping modulates the Au@CeO2 catalyst.

[0036] Figure 4 The gold catalyst supported on nano-cerium oxide in Example 1 ( Figure 4 (a1) Figure 4 (b1) and Figure 4 (c1)) and rubidium-doped cerium oxide nano-supported gold catalyst ( Figure 4 (a2) Figure 4 (b2) and Figure 4 (c2)) SEM-EDS comparison chart. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Example 1

[0043] 4g of glucose was dissolved in 50mL of deionized water, and then 20mg of chloroauric acid trihydrate was added. The mixture was stirred at room temperature for 30min until completely dissolved, forming a clear yellow solution A. Next, 2g of urea was dissolved in 40mL of deionized water, and then 10g of cerium chloride heptahydrate was added. The mixture was stirred at room temperature for 30min until completely dissolved, forming a clear solution A. Then, solution B was slowly introduced into solution A while stirring, and the mixture was stirred at room temperature for another 30min to form a clear yellow solution C. Solution C was then placed in a high-temperature reactor lined with polytetrafluoroethylene and subjected to hydrothermal reaction at 160℃ for 20h. After the hydrothermal reaction, the filtered residue was dried at 100℃ for 12h. Finally, the dried powder was calcined at 600℃ in air for 6h to obtain the catalyst Au@CeO2. Then, 500mg of the catalyst Au@CeO2 was dispersed in 100mL of a 0.1–0.7mol / L rubidium nitrate solution and stirred for impregnation modification at 300rpm for 30min. After modification, the solid-liquid separation filter residue was dried at 100℃ for 12 h. The dried powder was then calcined again at 600℃ in air for 6 h to obtain the catalyst Rb-Au@CeO2. The loading of nano-gold on rubidium-doped cerium oxide nanoparticles in the catalyst was 2 wt.%, and the rubidium doping amount was 0.01–0.02 wt.%. The catalytic reaction experiment was conducted by dissolving aniline in 1 ml of toluene solvent (aniline volume concentration 5%) and using 1 mL of hydrogen peroxide (aniline to hydrogen peroxide volume ratio 10:1). The catalytic reaction was carried out at a stirring speed of 300 rpm, with a catalyst addition of 50 mg: 0.1 mL, a catalytic time of 4–24 h, and a catalytic reaction temperature of 100℃. The experimental results are shown in Table 1. The catalytic reaction was the synthesis of azobenzene (A), azobenzene (B), and nitrobenzene (C) from aniline. The reaction equations are as follows:

[0044]

[0045] Table 1. Catalytic efficiency and selectivity of product A at different rubidium doping amounts and catalytic times of 4 h and 24 h.

[0046]

[0047] Catalytic experiments showed that the catalytic efficiency and target recognition of product A by catalyst Rb-Au@CeO2 were higher than those by catalyst Au@CeO2. Furthermore, the high rubidium doping concentration of catalyst Rb-Au@CeO2 maintained significant catalytic activity even after 24 hours, greatly improving its target recognition performance. For the 500 mg / L Au@CeO2 suspension, impregnation with rubidium nitrate at a concentration of 0.1 M to 0.5 M was optimal; excessively high rubidium nitrate concentrations increased costs. High catalytic activity was maintained even after 24 hours of catalysis. The highest catalytic conversion rate reached 100%, with a 92% selectivity for azobenzene oxide in the product.

[0048] Comparative Example 1

[0049] Compared with Example 1, all other conditions remained unchanged, except that the concentration of the Au@CeO2 catalyst suspension in the impregnation modification stage was changed from 500 mg / L to 750 mg / L. The catalyst Rb-Au@CeO2 was prepared by impregnation modification with 0.1–0.5 M rubidium nitrate for 24 h. The experimental results are shown in Table 2.

[0050] Table 2 Effect of different Au / CeO2 catalyst impregnation concentrations on the catalytic performance of (Rb-Au@CeO2)

[0051]

[0052] The results show that a catalyst Au@CeO2 concentration of 500 mg / L in the suspension improves catalyst performance during the impregnation modification process, while a concentration of 750 mg / L decreases catalytic performance. The catalytic activity increases with increasing Rb doping concentration, confirming the role of rubidium in the catalytic process. When the Au@CeO2 concentration in the suspension is >750 mg / L, the catalytic reaction of Rb-Au@CeO2 shows a decrease in catalytic rate, likely due to catalyst particle agglomeration at high concentrations. Therefore, a catalyst Au@CeO2 concentration of 200–500 mg / L in the suspension is optimal for the impregnation modification process.

[0053] Comparative Example 2

[0054] Compared with Example 1, other conditions remained unchanged. The concentration of the catalyst Au@CeO2 in the suspension during the impregnation modification process was 200 mg / L. The catalyst Rb-Au@CeO2 was prepared by impregnation in a 0.1 M rubidium nitrate solution. The ratio of Rb-Au@CeO2 added to aniline during the catalytic reaction was 200 mg to 1000 mg: 1 mL, and the catalytic time was 24 h. The experimental results are shown in Table 3.

[0055] Table 3 Catalytic efficiency and selectivity with different amounts of Rb-Au / CeO2 catalyst

[0056]

[0057] As shown in Table 3, the optimal dosage of rubidium-doped nano-cerium oxide supported gold catalyst (Rb-Au@CeO2) is 500–750 mg:1 mL. Although the yield of A increases at 1000 mg:1 mL, the catalytic efficiency decreases, meaning the catalytic performance of the reaction is reduced.

[0058] Comparative Example 3

[0059] With all other conditions unchanged compared to Example 1, a rubidium-doped cerium oxide nano-supported gold catalyst (Rb-Au@CeO2) was prepared by impregnating 200 mg / L nano-cerium oxide supported gold catalyst (Au@CeO2) in a 0.1 M rubidium nitrate solution. The Rb-Au@CeO2 addition ratio was 500 mg: 1 mL. The catalytic reaction temperature was 25–100 °C, and the catalytic time was 24 h. The experimental results are shown in Table 4.

[0060] Table 4 Catalytic efficiency and selectivity at different catalytic temperatures

[0061]

[0062] As shown in Table 4, with increasing temperature, the catalytic efficiency of aniline to azobenzene increased from 38% to 84.22%, and that of azobenzene oxide increased from 61.9% to 81.25%. At 25℃, the catalytic efficiency of aniline to azobenzene was 38%, and that of azobenzene oxide was 61.9%, while at 100℃, the catalytic efficiency of aniline was 84.22%, and that of azobenzene oxide was 81.25%. Generally, the catalytic performance increases with increasing temperature because there are more active sites at higher temperatures, resulting in higher catalytic performance. To ensure a high catalytic temperature, the catalytic reaction should be kept at as high a temperature as possible.

Claims

1. Use of a rubidium-doped nanoceria supported gold catalyst, characterized in that: The catalyst is applied to catalyze synthesis of aniline to synthesize an azo compound; The catalyst is composed of nano-gold loaded on rubidium-doped cerium oxide nanoparticles, and the loading amount of the nano-gold on the rubidium-doped cerium oxide nanoparticles is 1-3 wt.%. The rubidium-doped amount in the rubidium-doped cerium oxide nanoparticles is 0.01-0.02 wt.%. The preparation process of the catalyst is as follows: solution A containing dissolved glucose and gold source is mixed with solution B containing dissolved urea and cerium salt, and then hydrothermal reaction is performed to obtain a precursor; the precursor is calcined I to obtain nano-cerium oxide loaded gold particles; the nano-cerium oxide loaded gold particles are immersed in a rubidium salt solution, and then calcined II to obtain the catalyst.

2. The application of the rubidium-doped nano-cerium oxide loaded gold catalyst according to claim 1, characterized in that: The concentration of the glucose in the solution A is 5-8 wt.%. The mass ratio of the glucose to the gold source is (200-300):

1. The cerium salt includes cerium chloride and / or hydrate of cerium chloride. The concentration of the urea in the solution B is 5-8 wt.%. The mass ratio of the urea to the cerium salt in the solution B is (0.1-0.5):

1.

3. The use of a rubidium-doped nanoceria-supported gold catalyst according to claim 2, characterized in that: The hydrothermal reaction is performed at a temperature of 150-200℃ for 12-24h.

4. The use of a rubidium-doped nanoceria-supported gold catalyst according to claim 3, characterized in that: The calcination I is performed at a temperature of 550-650℃ for 4-10h.

5. The application of the rubidium-doped nano-cerium oxide loaded gold catalyst according to claim 3, characterized in that: The concentration of the nano-cerium oxide loaded gold particles in the rubidium salt solution is 200-500mg / L. The rubidium salt includes at least one of rubidium nitrate, rubidium chloride and rubidium sulfate.

6. The use of a rubidium-doped nanoceria-supported gold catalyst according to claim 5, characterized in that: The immersion is performed at a temperature of 25-90℃ for 30-60min at a rotation speed of 100-400rpm.

7. The use of a rubidium-doped nanoceria-supported gold catalyst according to claim 6, characterized in that: The calcination II is performed at a temperature of 550-650℃ for 4-10h.

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