Cerium dioxide catalysts and methods of making and using the same

Abstract

The application discloses a cerium dioxide catalyst and a preparation method and application thereof. The preparation method of the cerium dioxide catalyst comprises the following steps: synthesizing a metal organic framework precursor of Ce(COOH)3 by N,N-dimethylformamide and cerium salt in a nitrogen atmosphere, wherein the ratio of the N,N-dimethylformamide and the cerium salt is 1-5 mL / 1 g; and calcining the metal organic framework precursor in the nitrogen atmosphere to obtain the cerium dioxide catalyst. The sensor has a greatly improved sensitivity while realizing the detection of a large range, and the application effectively solves the problems of low defect concentration, activity and selectivity of the existing cerium dioxide catalyst.

Description

Technical Field

[0001] This invention belongs to the field of thermocatalysis technology, specifically a cerium dioxide catalyst, its preparation method, and its application. Background Technology

[0002] The role of oxygen vacancies in cerium dioxide in various heterogeneous catalytic reactions has been extensively studied, but our understanding of its function remains insufficient. Nanoscale cerium dioxide surfaces possess reversible Ce... 3+ / Ce 4+ Redox pairs give cerium dioxide a rich array of physicochemical properties. Modulating the oxygen vacancies in cerium dioxide alters its Lewis acid, Lewis base, and... Cerium dioxide possesses properties such as acidity and can serve as active sites. These reactive sites can form physical or chemical adsorption with different molecules, thereby affecting the activity and selectivity of catalytic reactions. Therefore, regulating oxygen defects in cerium dioxide is of great significance.

[0003] There are several methods for creating oxygen defects in cerium dioxide, including: 1) high-temperature heat treatment of CeO2 to control oxygen defects; 2) etching and reducing CeO2 using chemical reduction (such as ascorbic acid); 3) controlling the exposed crystal faces of synthesized cerium dioxide; and 4) elemental doping is also an important method for controlling oxygen defects. These methods inevitably require secondary treatment of the synthesized cerium dioxide, the use of strong alkaline reaction conditions, or the use of other chemical reagents such as ascorbic acid, which not only increases the synthesis cost but also makes the synthesis methods relatively complex. Therefore, there is an urgent need for a simpler method for synthesizing highly defective cerium dioxide. Furthermore, the activity and selectivity of catalysts used in epoxidation reactions need to be improved.

[0004] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a cerium dioxide catalyst, its preparation method, and its application, effectively solving the problems of low activity and selectivity in catalytic reactions.

[0006] The objective of this invention is achieved through the following technical solution: a method for preparing a cerium dioxide catalyst includes,

[0007] A metal-organic framework precursor of Ce(COOH)3 was synthesized in a nitrogen atmosphere via N,N-dimethylformamide and cerium salt, wherein the ratio of N,N-dimethylformamide to cerium salt was 1-5 mL / 1 g.

[0008] The metal-organic framework precursor was calcined in a nitrogen atmosphere to obtain a cerium dioxide catalyst.

[0009] In the method for preparing the cerium dioxide catalyst, the synthesis temperature is 100-150℃.

[0010] In the method for preparing the cerium dioxide catalyst, the synthesis time is 12-24 hours.

[0011] In the method for preparing the cerium dioxide catalyst, the temperature is increased to 350-600℃ at a rate of 4-6℃ / min during calcination for 1-3 hours.

[0012] In the method for preparing the cerium dioxide catalyst, the cerium salt includes cerium nitrate, cerium acetate, cerium sulfate, cerium chloride, cerium carbonate, cerium molybdate, cerium acetylacetone, or cerium ammonium nitrate.

[0013] A cerium dioxide catalyst is prepared by the aforementioned cerium dioxide catalyst preparation method.

[0014] In the cerium dioxide catalyst described above, the cerium dioxide catalyst is a cerium dioxide nanorod catalyst.

[0015] The cerium dioxide catalyst described herein is used to catalyze the epoxidation of olefin materials.

[0016] The cerium dioxide catalyst is used to catalyze the oxidation of cyclooctene.

[0017] The cerium dioxide catalyst is uniformly dispersed in a cyclooctene solution; oxygen is introduced into the cyclooctene solution under high pressure, and the reaction is carried out under stirring at 80-100℃.

[0018] Compared with existing technologies, this invention has the following advantages: This invention uses DMF as a solvent to synthesize cerium dioxide materials, resulting in a high defect concentration on its surface. This step is simple, requires mild conditions, and uses readily available and inexpensive raw materials. This cerium dioxide material has a high oxygen defect concentration, resulting in high catalytic efficiency and a catalytic conversion rate exceeding 99%. In the catalytic oxidation of cyclooctene, oxygen or air is used as the oxygen source, aligning with the principles of green chemistry. Compared to existing catalysts used for the epoxidation of cyclooctene, this invention exhibits better activity and selectivity. The reaction time required to achieve a cyclooctene conversion rate exceeding 99% and a selectivity for cyclooctene oxidation exceeding 90% is only 5 hours, significantly improving yield and reducing production costs. Attached Figure Description

[0019] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0020] In the attached diagram:

[0021] Figure 1 Transmission electron microscopy images of (a) cerium dioxide (NP) synthesized by ordinary calcination and (b) cerium dioxide (CeO2-D) synthesized by DMF and cerium salt provided in Example 1;

[0022] Figure 2 High-resolution transmission image of the CeO2-D catalyst provided in Example 1;

[0023] Figure 3 X-ray photoelectron spectroscopy (XPS) of the NP(a) and CeO2-D catalysts provided in Example 1;

[0024] Figure 4 The graph shows the effect of the two catalysts, NP and CeO2-D, provided in Example 2 on the epoxidation of cyclooctene.

[0025] Figure 5 The stability diagram of the CeO2-D catalyst provided in Example 2 for the epoxidation of cyclooctene is shown.

[0026] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0027] The following will refer to the appendix. Figures 1 to 5 Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0028] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0029] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0030] To better understand, such as Figures 1 to 5 As shown, a method for preparing a cerium dioxide catalyst includes: adding cerium salt to DMF and stirring to dissolve it; then transferring the mixture to a sealed reactor and purging it with nitrogen gas; reacting at 100°C for 10 hours; naturally cooling to room temperature; washing the resulting product several times alternately with water and ethanol until all DMF is removed; then drying the solid in a vacuum drying oven at 60°C for 12 hours; and finally calcining the solid powder in a N2 atmosphere for 2 hours to obtain the cerium dioxide catalyst. This catalyst can effectively solve the problems of low defect concentration, low activity, and low selectivity of existing cerium dioxide catalysts.

[0031] In one embodiment, the preparation method includes the following steps:

[0032] 1. Synthesis of Ce(COOH)3 MOF precursor by DMF and cerium salt in N2 atmosphere;

[0033] 2. The MOF precursor of Ce(COOH)3 was calcined in a nitrogen atmosphere to obtain the final cerium dioxide nanorod catalyst.

[0034] The cerium dioxide catalyst prepared by the above method not only has a high oxygen defect concentration but also exhibits a stable structure under high-temperature conditions. Furthermore, the preparation process is convenient, low-cost, and suitable for large-scale production. Compared with cerium dioxide catalysts synthesized by traditional calcination, the cerium dioxide catalyst synthesized via DMF shows a 3.5-fold increase in activity and higher selectivity in the catalytic reaction. This provides an effective method for the efficient preparation of epoxidation reaction catalysts.

[0035] Furthermore, the cerium salt in step 1 includes various anionic cerium salts, such as cerium nitrate, cerium acetate, cerium sulfate, cerium chloride, cerium carbonate, cerium molybdate, cerium acetylacetone, and cerium ammonium nitrate.

[0036] Furthermore, the synthesis temperature in step 1 is 100-150℃.

[0037] Furthermore, in step 1, the DMF / cerium salt synthesized is >1 mL / 1 g.

[0038] Furthermore, the drying temperature in step 1 is 60-80℃.

[0039] Furthermore, the synthesis reaction time in step 1 is 6-24 hours.

[0040] In the above schemes, different synthesis temperatures and synthesis times will affect the surface oxygen defect concentration and morphology of cerium dioxide materials, thus affecting the catalytic effect.

[0041] Furthermore, the MOF calcination of the precursor in step 2 is carried out in an N2 atmosphere.

[0042] Furthermore, during calcination in step 2, the temperature is increased to 350-600℃ at a rate of 5℃ / min and calcined for 1-3 hours.

[0043] In the above scheme, calcination at 350-600℃ can transform the precursor MOF structure into a cerium dioxide crystal structure, giving it redox properties and improving the catalytic effect.

[0044] A high-defect cerium dioxide catalytic material was prepared using the method described above.

[0045] Furthermore, the application of cerium dioxide catalytic materials with high defects as catalysts.

[0046] Furthermore, the catalyst is used to catalyze the epoxidation reaction of cyclooctene.

[0047] The specific catalytic operation process is as follows:

[0048] 1. The prepared cerium dioxide material is uniformly dispersed in an organic solvent of cyclooctene, where cyclooctene is both a substrate and a solvent;

[0049] 2. Introduce oxygen into the mixture under high pressure and carry out the reaction at 100°C with stirring.

[0050] Example 1

[0051] A method for preparing a catalytic oxidation material based on synthesized high-defect cerium dioxide includes the following steps:

[0052] 1. Preparation of cerium dioxide precursor Ce(COOH)3

[0053] Dissolve 10g of cerium salt in 10mL of DMF solution and stir at room temperature. Transfer the solution to a high-pressure reactor, wash three times with N2, and adjust the pressure to 0-1MPa. React the solution in a reactor at 100℃ for 24h. After the reaction is complete, allow it to cool naturally to room temperature. Wash the obtained solid with ethanol to remove the remaining DMF. Finally, place the obtained solid powder in a vacuum drying oven and dry at 60℃.

[0054] 2. Preparation of cerium dioxide catalyst CeO2-D:

[0055] The solid powder obtained in step 1 was heated to 350°C in N2 at a rate of 5°C / min and calcined for 2 hours to obtain the final product.

[0056] Example 2

[0057] A method for preparing a catalytic oxidation material based on synthesized high-defect cerium dioxide includes the following steps:

[0058] 1. Preparation of cerium dioxide nanoparticles (NP)

[0059] 5g of accurately weighed Ce(NO3)3·6H2O solid was calcined in a muffle furnace at 10℃ / min to 500℃ for 2h to obtain the NP catalyst.

[0060] Test case

[0061] I. Catalytic reaction tests were performed on the catalysts prepared in Example 1 and Example 2. Specific test results are shown in the appendix. Figure 4 .

[0062] Figure 1 TEM characterization results for the NP catalyst and CeO2-D catalyst are shown in the figures below. Figure 1 a and Figure 1 b. Figure 1 b shows a cerium dioxide nanorod structure.

[0063] Figure 2 This is a high-resolution TEM image of the CeO2-D catalyst. Meanwhile, the measured lattice fringe spacings are 0.198 nm and 0.316 nm, which correspond to the (111) and (110) crystal planes of the CeO2 nanoparticles in the high-resolution TEM image, respectively. This indicates that the cerium dioxide material mainly grows along the 110 and 111 planes.

[0064] Figure 3 XPS images of the NP catalyst and the CeO2-D catalyst. Simultaneously, analysis of their Ce... 3+ Content of Ce in NP and CeO2-D catalysts 3+The contents were 15.4% and 31.5% respectively, which indicates that CeO2-D material has a high concentration of surface defects.

[0065] II. The catalysts prepared in Example 1 and Comparative Example 2 were used to catalyze the epoxidation of cyclooctene to prepare cyclooctene oxide, and the specific operations are as follows:

[0066] 1. Disperse 5 mg of CeO2-D catalyst material uniformly in 1 mL of cyclooctene.

[0067] 2. Transfer the mixture from step 1 above to a 500 mL autoclave, wash it three times with 1 MPa O2, and then carry out the reaction in a 1 MPa O2 atmosphere with magnetic stirring and the temperature controlled at 100 °C.

[0068] 3. Quantitative analysis of the liquid phase composition was performed using gas chromatography, and the conversion rate of cyclooctene and the selectivity of oxidized cyclooctene were recorded.

[0069] from Figure 3 As can be seen, the CeO2-D catalyst achieved a 90.6% conversion rate of cyclooctene after 4 hours of reaction. Under the same reaction conditions, the NP catalyst achieved only a 25.9% conversion rate after 4 hours. The conversion rate of CeO2-D was 3.5 times higher than that of NP. Therefore, the CeO2-D catalyst synthesized via DMF can significantly improve its catalytic oxidation activity.

[0070] In addition to significantly improving activity, CeO2-D catalysts also enhance the selectivity for cyclooctene oxidation. For example... Figure 3 As shown, the selectivity for cyclooctene oxidation remained at 91.2% during the reaction. Under the same reaction conditions, the NP catalyst achieved a conversion rate of 25.9% for cyclooctene oxidation, but only a selectivity of 75.7%. Therefore, the CeO2-D catalyst can simultaneously improve both the catalytic activity and selectivity of cyclooctene oxidation to cyclooctene oxide.

[0071] III. Catalyst Cyclic Stability Test

[0072] Catalyst stability is also an important factor in evaluating catalyst performance. 5 mg of CeO2-D catalyst was weighed and added to 1 mL of cyclooctene liquid. The oxygen pressure was 1 MPa, and the reaction was carried out at 100 °C. One reaction cycle was 4 hours. The catalyst could be separated by centrifugation and recycled without further treatment. Three cycles were tested.

[0073] The CeO2-D catalyst achieved cyclooctene conversions of 91.6%, 90.3%, and 90.7% in the first, second, and third cycles, respectively. Figure 5As shown, this indicates that the catalyst possesses good catalytic stability. Therefore, the CeO2-D catalyst exhibits high catalytic activity and selectivity, as well as good stability, while simultaneously catalyzing the oxidation of cyclooctene.

[0074] The above experimental results show that the CeO2-D catalyst has high reusability in the oxidation of cyclooctene to prepare cyclooctene oxide.

[0075] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. The application of a cerium dioxide catalyst in the oxidation of cyclooctene to prepare cyclooctene oxide, characterized in that, The preparation method of the cerium dioxide catalyst includes the following steps: A metal-organic framework precursor of Ce(COOH)3 was synthesized in a nitrogen atmosphere via N,N-dimethylformamide and cerium salt, wherein the ratio of N,N-dimethylformamide to cerium salt was 1-5 mL / 1 g. The cerium salt was dissolved in an N,N-dimethylformamide solution and stirred at room temperature to dissolve. The solution was then transferred to a high-pressure reactor, washed three times with N2, and the pressure was adjusted to 0-1 MPa. The synthesis temperature was 100-150 °C. The metal-organic framework precursor was calcined in a nitrogen atmosphere to obtain a cerium dioxide nanorod catalyst. During calcination, the temperature is increased to 350-600℃ at a rate of 4-6℃ / min and calcined for 1-3 hours.

2. The application according to claim 1, characterized in that, The synthesis time is 12-24 h.

3. The application according to claim 1, characterized in that, Cerium salts include cerium nitrate, cerium acetate, cerium chloride, cerium acetylacetone, or cerium ammonium nitrate.

4. The application according to claim 1, characterized in that, The cerium dioxide catalyst is uniformly dispersed in a cyclooctene solution; oxygen is introduced into the cyclooctene solution under high pressure, and the reaction is carried out under stirring at 80-100℃.

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