A cobalt-doped spherical ceria catalyst, a preparation method and application thereof

Abstract

The application discloses a cobalt-doped spherical ceria catalyst and a preparation method and application thereof. In the catalyst, cobalt atoms are dispersed in the ceria crystal lattice in a single atom form and form an oxygen-bridged Co-O-Ce interface structure. The ceria carrier is a nanometer spherical morphology formed by 10-20 nm nanoparticles. The BET specific surface area is 30-35 m 2 / g, and the mesopore size is 2-20 nm. When the catalyst is used for solvent-free ethylbenzene oxidation, the ethylbenzene conversion rate is 67.9%, the acetophenone selectivity is 88.3%, the reaction rate per unit area is 9.1*10 7 mol·m 2 ⁻ 1 ·s⁻ 1 , and the performance is stable after 5 cycles. The application has a unique stacking-limited structure and an atomic-level dispersed Co-O-Ce interface, and has excellent catalytic performance and a green preparation process.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a cobalt atom-doped spherical cerium dioxide catalyst, its preparation method, and its application in the selective oxidation of ethylbenzene to acetophenone using molecular oxygen as an oxidant under solvent-free and additive-free conditions. Background Technology

[0002] Acetophenone is an important fine chemical intermediate, widely used in the production of fragrances, pharmaceuticals, and pesticide synergists. Traditionally, the industry primarily uses homogeneous catalysts (such as cobalt and manganese salts) in conjunction with peroxides or stoichiometric oxidants (such as chromates and permanganates) to oxidize ethylbenzene. These methods suffer from problems such as difficulty in catalyst separation and the generation of large amounts of toxic waste. Heterogeneous catalytic systems using molecular oxygen as an oxidant offer advantages in terms of being green and sustainable.

[0003] Cerium dioxide (CeO2) is valued for its excellent oxygen storage capacity and reversible CeO2 oxidation. 3+ / Ce 4+ Redox cycles have attracted widespread attention. However, pure CeO2 has weak activation ability for the CH bonds of ethylbenzene, and the conversion rate of ethylbenzene is usually below 5%. Patent CN117504898B discloses a lanthanum-cobalt composite catalyst with the composition of La2O2SO4, Co4S3, and Co3O4. When used for solventless ethylbenzene oxidation, it achieves a conversion rate of 87.3% and a selectivity of 89.7%. However, this catalyst contains sulfur, has a complex composition, and cobalt exists in the form of Co3O4 and Co4S3, rather than being a single-atom dispersion. Patent CN121467082A discloses a single-atom Fe catalyst anchored on a nitrogen-doped carbon support by Fe-N coordination bonds. When used for ethylbenzene oxidation, it achieves a conversion rate of 98.3% and a selectivity of 99.8%. However, this catalyst requires tert-butyl hydroperoxide (TBHP) as an oxidant, rather than clean molecular oxygen, and the carbon support has poor stability under high-temperature aerobic conditions.

[0004] Patent CN117619382B discloses a Pd / CNb2O5 catalyst for the solvent-free photocatalytic oxidation of ethylbenzene to acetophenone, achieving a conversion rate of 67.4% and a selectivity of 97.7%. However, this catalyst uses the precious metal Pd, resulting in high cost, and requires UV / Vis excitation, limiting its industrial application. Lanzhou University of Technology has disclosed a Co-MOF-derived [CoO] catalyst... xThe / NCS]@Co-MOF catalyst (CN 120054639 A) achieves a conversion of 98.3% and a selectivity of 99.8% for ethylbenzene oxidation. However, its preparation is cumbersome (requiring multiple hydrothermal, carbonization, and aging processes) and requires carbon dioxide assistance and tert-butyl hydroperoxide (TBHP) as the oxidant. Palli et al. (Res. Chem. Intermed., 2022, 48, 471-490) reported a mesoporous Ce 0.9 Co 0.1 An O2 solid solution catalyst was used for the solventless oxidation of ethylbenzene to acetophenone, achieving a conversion rate of 60% and a selectivity of 87%, with a normalized reaction rate of only 3.2 × 10⁻⁻⁻⁴. 7 mol·m⁻ 2 ·s⁻ 1 Furthermore, its cycle stability is poor, with the conversion rate decreasing by about 5 percentage points after 5 cycles, indicating continuous inactivation, which limits its practical application potential.

[0005] In summary, the existing technologies for the oxidation of ethylbenzene to prepare acetophenone have the following shortcomings: (1) Noble metal catalysts are expensive, and in non-noble metal catalysts (such as Co3O4, Co / CeO2), cobalt species are mostly in the form of clusters or nanoparticles, resulting in low atom utilization; (2) Most catalytic systems require organic solvents, free radical initiators or special oxidants (such as TBHP), which do not meet the requirements of green chemistry; (3) The intrinsic activity (reaction rate per unit area) of existing Co / CeO2 catalysts in the oxidation of ethylbenzene is low, and the cycle stability is insufficient. Summary of the Invention

[0006] Objectives of this invention: The present invention aims to provide an atomically dispersed Co / CeO2 catalyst capable of efficiently and stably catalyzing the oxidation of ethylbenzene to acetophenone under mild conditions without solvents or additives, using molecular oxygen as an oxidant; a second objective of this invention is to provide a method for preparing a cobalt-doped cerium dioxide catalyst; and a third objective of this invention is to provide the application of a cobalt-doped spherical cerium dioxide catalyst in the selective oxidation of ethylbenzene to acetophenone under solvent-free and free radical initiator-free conditions.

[0007] Technical solution: The cobalt-doped spherical cerium dioxide catalyst of this invention has cobalt atoms dispersed in the cerium dioxide lattice in the form of single atoms, forming an oxygen-bridged Co-O-Ce interface structure; the cerium dioxide support is a nanosphere morphology composed of nanoparticles with a particle size of 10~20 nm, and its BET specific surface area is 30~35 m². 2 / g, and the mesopores formed by the stacking have a diameter of 2~20 nm.

[0008] Preferably, the surface Co of the cobalt-doped spherical cerium dioxide catalyst is... 2+ / Co3+ The atomic ratio is 2.2~2.3, Ce 3+ / Ce 4+ With an atomic ratio of 0.50~0.55, the surface adsorbed oxygen and lattice oxygen are O ads / O latt The atomic ratio is 2.7~2.8.

[0009] Preferably, in the XRD pattern of the cobalt-doped spherical cerium dioxide catalyst, the (111) crystal plane diffraction peak of CeO2 is shifted at a higher angle by ≥0.25° relative to pure spherical CeO2, and the lattice shrinkage rate is ≥0.8%.

[0010] Preferably, in the Co K-edge EXAFS spectrum of the catalyst, there is a Co-Ce coordination peak at 2.40~2.50 Å and no Co-Co coordination peak at 2.10~2.20 Å; the Co-O bond coordination number is 4.4~4.8 and the Co-O bond length is 1.90~1.96 Å.

[0011] Preferably, the cobalt content is 3-6 wt%.

[0012] Preferably, in the NH3-TPD spectrum of the catalyst, there is a strong acid desorption peak in the range of 500~550℃, and its area accounts for ≥15% of the total desorption peak area.

[0013] The preparation method of the above-mentioned cobalt-doped spherical cerium dioxide catalyst according to the present invention includes the following steps:

[0014] (1) Dissolve cerium salt in water, add alkaline solution, and after aging, hydrothermal treatment, washing, drying and calcination, s-CeO2 with nanosphere morphology is obtained; wherein, the hydrothermal temperature is 120~130℃, and the alkaline solution used is sodium hydroxide solution with a concentration of 5~7 mol / L;

[0015] (2) The s-CeO2 support with nanosphere morphology obtained in step (1) is dispersed with cobalt salt in deionized water and stirred for 1-2 hours to obtain mixture A; the cobalt salt is cobalt nitrate, and the theoretical doping amount of cobalt is 3-6 wt%;

[0016] (3) Dissolve sodium borohydride in deionized water to obtain solution B;

[0017] (4) Add solution B dropwise to mixture A at a rate of 0.5~1.0 mL / min while stirring, and react at room temperature for 1~3 hours. Centrifuge within 10 minutes after the reaction is completed.

[0018] (5) Centrifuge to separate the solid, wash it with deionized water and anhydrous ethanol alternately 3 to 5 times, and then dry it under vacuum to obtain cobalt-doped spherical cerium dioxide catalyst.

[0019] The application of the cobalt-doped spherical cerium dioxide catalyst described in this invention in the selective oxidation of ethylbenzene to acetophenone under solvent-free and free radical initiator-free conditions.

[0020] Preferably, cobalt-doped spherical cerium dioxide catalyst and ethylbenzene are added to a high-pressure reactor, oxygen is introduced to a pressure of 0.5~0.7 MPa, and the reaction is stirred at 120~140℃ for 3~6 hours; wherein the mass ratio of cobalt-doped spherical cerium dioxide catalyst to ethylbenzene is 1:40~1:60; after the reaction is completed, the cobalt-doped spherical cerium dioxide catalyst is separated by centrifugation to obtain a product mixture containing acetophenone.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Unique "stacking-confined" structural design: The present invention is the first to combine the stacking morphology of nanospheres with atomically dispersed cobalt doping. The 2-20 nm mesopores formed by the stacking of spherical nanoparticles enrich Co through capillary action. 2+ The high-density lattice defects and low-coordination sites at the ion-particle interface are Co 2+ It provides a preferred substitution channel and anchoring point. This "stack-induced lattice doping" mechanism is different from the traditional impregnation method in which the metal is mainly loaded on the outer surface. It is the structural basis for the present invention to achieve atomic-level dispersion at a high loading of 5 wt%; (2) Atomic-level dispersed Co-O-Ce interface: Cobalt atoms are doped into the cerium dioxide lattice in the form of single atoms by the room temperature sodium borohydride reduction method to form an oxygen-bridged Co-O-Ce structure. In the XRD pattern, the (111) crystal plane diffraction peak of CeO2 is shifted at a higher angle by ≥0.25° relative to the pure spherical CeO2, and the lattice shrinkage rate is ≥0.8%; this shows that Co is successfully incorporated into the CeO2 lattice rather than forming an independent crystal phase. EXAFS confirmed the absence of Co-Co coordination peaks and reduced the Co-O bond coordination number to 4.4~4.8, proving that cobalt exists in an atomically dispersed form; (3) Highly efficient activation of CH bonds: In the NH3-TPD spectrum, the catalyst of this invention exhibits a significant strong acid desorption peak in the range of 500~550℃, with its area accounting for ≥15% of the total desorption peak area. This strong acid site originates from atomically dispersed cobalt species in a spherical cerium dioxide lattice, providing a strong adsorption and polarization center for ethylbenzene molecules. It is this strong acidity that enables the catalyst to efficiently activate the inert CH bonds of ethylbenzene under solvent-free conditions, significantly reducing the apparent activation energy of the reaction to 32.6 kJ·mol⁻ 1The catalytic performance is far lower than that of other morphologies of Co / CeO2 catalysts and traditional Co3O4 catalysts, laying a key kinetic foundation for subsequent oxidation reactions; (4) Excellent catalytic performance: Under solvent-free and additive-free conditions (such as free radical initiators), with molecular oxygen as the oxidant, the ethylbenzene conversion rate can reach 67.9% and the acetophenone selectivity can reach 88.3% after 5 hours of reaction at 130℃ and 0.6 MPa O2. Its reaction rate per unit area (9.1×10⁻ 7 mol·m⁻ 2 ·s⁻ 1 (5) Unique superoxide radical-dominated reaction pathway: Free radical capture experiments proved that in the catalytic oxidation reaction, superoxide radical (O2•⁻) is the only active oxygen species, and the contribution rate of hydroxyl radical (•OH) to the reaction is ≤5%; CeO2 acts as an electron buffer, and in the reaction process, CeO2 can be used to catalyze the reaction by activating the superoxide radical (O2•⁻) to ... 3+ ⇌ Ce 4+ The reversible transformation of the catalyst accepts electrons from Co and transfers them to molecular oxygen, thereby maintaining the valence state cycle of the Co active center; (6) Stable recycling performance: the catalyst has a unit area reaction rate of ≥9.1×10⁻ in the ethylbenzene oxidation reaction. 7 mol·m⁻ 2 ·s⁻ 1 Furthermore, the catalyst, after centrifugation, ethanol washing, and vacuum drying at 80℃, is directly recycled. After five consecutive cycles, the ethylbenzene conversion rate decreases by no more than 0.5%. 2+ / Co 3+ atomic ratio, Ce 3+ / Ce 4+ atomic ratio and O ads / O latt The change in atomic ratio is ≤2%. After five consecutive uses, the activity and selectivity of the catalyst did not decrease significantly. The morphology, crystal phase, cobalt valence state and oxygen vacancy concentration all returned to their initial values, showing excellent cycle stability and industrial application potential. (7) Green and mild preparation process: The present invention uses room temperature sodium borohydride reduction, without any high temperature calcination or hydrogen reduction treatment, which greatly reduces energy consumption. No template agent or surfactant is used, avoiding environmental pollution. The preparation process is simple and easy to scale up. Attached Figure Description

[0022] Figure 1 This is a SEM image of the Co / s-CeO2 catalyst in Example 1 of the present invention;

[0023] Figure 2 The XRD pattern of the Co / s-CeO2 catalyst in Example 1 of this invention;

[0024] Figure 3 This is a pore size distribution diagram of the Co / s-CeO2 catalyst in Example 1 of the present invention;

[0025] Figure 4 The image shows the NH3-TPD of the Co / s-CeO2 catalyst in Example 1 of this invention.

[0026] Figure 5 This is the R-space diagram of the Co / s-CeO2 catalyst in Example 1 of the present invention;

[0027] Figure 6 XPS diagram of the Co 2P orbitals of the Co / s-CeO2 catalyst in Example 1 of this invention;

[0028] Figure 7 XPS plot of Ce 3d orbitals of the Co / s-CeO2 catalyst in Example 1 of this invention;

[0029] Figure 8 XPS diagram of the O 1s orbitals of the Co / s-CeO2 catalyst in Example 1 of this invention;

[0030] Figure 9 This is a graph showing the change in reaction performance of the Co / s-CeO2 catalyst under low conversion (<10%) conditions over time in Example 1 of this invention.

[0031] Figure 10 The lnr ~ 1 / T Arrhenius fitting curve for the ethylbenzene oxidation reaction on the Co / s-CeO2 catalyst in Example 1 of this invention;

[0032] Figure 11 This is a graph showing the free radical capture experiment results of the Co / s-CeO2 catalyst catalyzing the ethylbenzene oxidation reaction in Example 1 of this invention;

[0033] Figure 12 The reaction performance of the Co / s-CeO2 catalyst in Example 1 of this invention after 5 cycles;

[0034] Figure 13 This is a SEM image of the Co / s-CeO2 catalyst after 5 cycles in Example 1 of this invention;

[0035] Figure 14 The XRD pattern of the Co / s-CeO2 catalyst after 5 cycles in Example 1 of this invention;

[0036] Figure 15 This is an XPS diagram of the Co 2P orbitals of the Co / s-CeO2 catalyst after 5 cycles in Example 1 of this invention;

[0037] Figure 16This is an XPS image of Ce 3d orbitals after 5 cycles of the Co / s-CeO2 catalyst in Example 1 of this invention;

[0038] Figure 17 This is an XPS diagram of the O 1s orbital of the Co / s-CeO2 catalyst after 5 cycles in Example 1 of this invention. Detailed Implementation

[0039] Example 1

[0040] (1) Preparation of s-CeO2 support: 2.17 g of cerium nitrate hexahydrate was dissolved in 20 mL of deionized water. 60 mL of 6 mol / L NaOH solution was added dropwise under stirring. After aging at room temperature for 30 min, the solution was transferred to a 100 mL high-pressure autoclave lined with polytetrafluoroethylene and hydrothermally treated at 125 °C for 24 h. The precipitate was collected by centrifugation, washed, dried at 80 °C for 12 h, and calcined at 500 °C for 3 h to obtain nanospheres of s-CeO2.

[0041] (2) Preparation of Co / s-CeO2 catalyst: 200 mg of s-CeO2 obtained in step (1) and 98.76 mg of cobalt nitrate hexahydrate were dispersed in 30 mL of deionized water and stirred at 600 rpm for 1 h to form mixture A. 30 mg of sodium borohydride was dissolved in 2 mL of deionized water and sonicated for 2 min to obtain solution B. Solution B was added dropwise to mixture A at a rate of approximately 0.8 mL / min under continuous stirring, and the reaction was carried out at room temperature for 2 h. After the reaction was completed, the solid was immediately separated by centrifugation (8000 rpm, 5 min), washed three times alternately with deionized water and anhydrous ethanol, and dried under vacuum at 80 °C for 24 h to obtain the Co / s-CeO2 catalyst. The cobalt content was determined to be 5.0 wt% by ICP.

[0042] (3) Ethylbenzene oxidation reaction: 1 mL of ethylbenzene (about 0.86 g) and 20 mg of Co / s-CeO2 catalyst were added to a 25 mL stainless steel autoclave lined with polytetrafluoroethylene. Oxygen was introduced to 0.6 MPa, and the reaction was carried out at 130 °C and 600 rpm for 5 h. After the reaction was completed, the catalyst was separated by centrifugation, and the liquid product was analyzed by gas chromatography.

[0043] Example 2

[0044] (1) The preparation of the s-CeO2 support is the same as in Example 1.

[0045] (2) Preparation of Co / s-CeO2 catalyst: The amount of cobalt salt was adjusted to 49.38 mg (theoretical loading 2.5 wt%), and other parameters were the same as in Example 1. The cobalt content was determined to be 2.5 wt% by ICP.

[0046] (3) The ethylbenzene oxidation reaction is the same as in Example 1.

[0047] Example 3

[0048] (1) The preparation of the s-CeO2 support is the same as in Example 1.

[0049] (2) Preparation of Co / s-CeO2 catalyst: The amount of cobalt salt was adjusted to 197.52 mg (theoretical loading 10 wt%), and other parameters were the same as in Example 1. The cobalt content was determined to be 9.8 wt% by ICP.

[0050] (3) The ethylbenzene oxidation reaction is the same as in Example 1.

[0051] Example 4

[0052] (1) The preparation of the s-CeO2 support is the same as in Example 1.

[0053] (2) The preparation of the Co / s-CeO2 catalyst is the same as in Example 1.

[0054] (3) Ethylbenzene oxidation reaction: The temperature was changed to 120℃, and the rest was the same as in Example 1.

[0055] Example 5

[0056] (1) The preparation of the s-CeO2 support is the same as in Example 1.

[0057] (2) The preparation of the Co / s-CeO2 catalyst is the same as in Example 1.

[0058] (3) Ethylbenzene oxidation reaction: The oxygen pressure was changed to 0.4 MPa, and the rest was the same as in Example 1.

[0059] Example 6

[0060] (1) The preparation of the s-CeO2 support is the same as in Example 1.

[0061] (2) The preparation of the Co / s-CeO2 catalyst is the same as in Example 1.

[0062] (3) Ethylbenzene oxidation reaction: The reaction time was changed to 3 h, and the rest was the same as in Example 1.

[0063] Comparative Example 1 (pure Co3O4)

[0064] The ethylbenzene oxidation reaction was performed using commercially available Co3O4 (1.4 mg, equivalent to the mass of Co in Example 1), as in Example 1. The results are shown in Table 1.

[0065] Comparative Example 2 (pure s-CeO2)

[0066] The ethylbenzene oxidation reaction was performed in the same manner as in Example 1, using pure s-CeO2 instead of Co / s-CeO2. The results are shown in Table 1.

[0067] Comparative Example 3 (Prepared by Impregnation Method)

[0068] Co / s-CeO2-imp was prepared by impregnation: s-CeO2 was impregnated in a cobalt nitrate aqueous solution, stirred for 12 h, evaporated to dryness, dried at 100℃ for 12 h, and calcined at 500℃ for 4 h. ICP analysis showed a cobalt content of 5.0 wt%. EXAFS showed a distinct Co-Co coordination peak. The ethylbenzene oxidation reaction was the same as in Example 1, and the results are shown in Table 1.

[0069] Comparative Example 4 (CoO / CeO2 from the literature)

[0070] CoO / CeO2 was synthesized according to the method described in ACS Materials Lett. 2022, 4, 2572-2578. The ethylbenzene oxidation reaction was the same as in Example 1, and the results are shown in Table 1.

[0071] Comparative Example 5 (Non-Stacked Nanoparticle Carrier)

[0072] The method of Example 1 was followed, but the spherical CeO2 support was replaced with one having a similar specific surface area (31.5 m²). 2 CeO2 nanoparticles (dispersed, non-aggregated) without a stacking structure were used. ICP analysis showed a cobalt loading of 5.0 wt%. EXAFS characterization revealed a distinct Co-Co coordination peak at 2.10–2.25 Å, indicating that cobalt failed to achieve atomic-level dispersion. The ethylbenzene oxidation reaction was performed as in Example 1, and the results are shown in Table 1. This comparative example demonstrates that a high specific surface area alone is insufficient to achieve atomic-level cobalt dispersion; the specific stacking structure of the spherical nanoparticles is crucial.

[0073] Comparative Example 6 (Aging Treatment Control)

[0074] The method of Example 1 was followed, but the mixture was aged for 12 hours after the reduction reaction was completed before centrifugation. EXAFS showed the appearance of Co-Co coordination peaks, and the ethylbenzene conversion rate decreased to 42.1% (see Table 1). This demonstrates that not aging is key to preventing Co aggregation.

[0075] Comparative Example 7 (rapid addition of sodium borohydride)

[0076] The method of Example 1 was followed, but the sodium borohydride solution was added rapidly in one go (instead of slowly dripping). EXAFS showed the appearance of Co-Co coordination peaks, and the ethylbenzene conversion decreased to 38.7% (see Table 1). This demonstrates that slow dripping is a necessary condition for achieving atomic-level dispersion.

[0077] I. Performance Testing

[0078] Table 1 shows the conversion rate, selectivity, and reaction rate per unit area for Examples 1-6 and Comparative Examples 1-7.

[0079] Reaction rate determination (using the catalyst of Example 1 as an example): The initial reaction rate was determined under low conversion conditions (<10%). After normalization by specific surface area, the reaction rate was 9.1 × 10⁻⁻⁻⁶. 7 mol·m⁻ 2 ·s⁻ 1 (like Figure 9 (As shown).

[0080] Apparent activation energy determination: Using Arrhenius linear fitting with lnr against 1 / T, the apparent activation energy of the ethylbenzene oxidation reaction on the Co / s-CeO2 catalyst described in this invention was determined to be 32.6 kJ·mol⁻¹. 1 (like Figure 10 (As shown).

[0081] Free radical capture experiment: PBQ and TBA were added to the reaction system respectively. The results showed that PBQ completely inhibited the reaction (conversion rate 0%), while TBA showed almost no inhibition (conversion rate 67.3%), proving that superoxide radicals were the only reactive species (e.g., Figure 11 (As shown).

[0082] Table 1

[0083] Example 1 Standard conditions 5.0 67.9 88.3 9.1 Example 2 Co doping 2.5 wt% 2.5 47.7 88.2 6.4 Example 3 Co doping 10 wt% 9.8 64.7 86.5 8.7 Example 4 Reaction temperature 120℃ 5.0 55.3 90.1 7.4 Example 5 <![CDATA[O2 pressure 0.4 MPa]]> 5.0 58.5 88.2 7.8 Example 6 Reaction time 3 h 5.0 64.3 88.5 9.1 Comparative Example 1 <![CDATA[Pure Co3O4]]> — 4.5 85.3 1.4 Comparative Example 2 <![CDATA[Pure s-CeO2]]> 0 3.3 82.5 1.1 Comparative Example 3 Preparation by impregnation method 5.0 28.6 83.1 3.7 Comparative Example 4 <![CDATA[Literature CoO / CeO2]]> 5.0 23.5 86.2 3.1 Comparative Example 5 Non-stacking nanoparticle carriers 5.0 31.2 84.5 3.5 Comparative Example 6 After reduction, age for 12 hours 5.0 42.1 80.4 4.6 Comparative Example 7 Add sodium borohydride quickly 5.0 38.7 76.1 4.2 Comparison of different morphologies <![CDATA[cubic CeO2 (c-CeO2)]]> 5.0 42.3 83.2 3.0 Comparison of different morphologies <![CDATA[Granular CeO2 (p-CeO2)]]> 5.0 59.8 84.1 8.6 Comparison of different morphologies <![CDATA[Spindle-shaped CeO2 (f-CeO2)]]> 5.0 50.3 83.8 6.2

[0084] II. Catalyst Characterization and Mechanism Analysis

[0085] The Co / s-CeO2 catalyst prepared in Example 1 was characterized as follows:

[0086] SEM revealed that it has a spherical morphology composed of nanoparticles with a particle size of 10-20 nm (e.g., Figure 1 (As shown).

[0087] XRD analysis revealed characteristic diffraction peaks of CeO2 with a cubic fluorite structure, without any Co3O4 or CoO phases; compared to pure s-CeO2, the (111) peak shifted to a higher angle by 0.29°, and the lattice shrinkage was 0.96%. This indicates that Co was successfully incorporated into the CeO2 lattice rather than forming an independent crystalline phase (e.g., ...). Figure 2 (As shown).

[0088] The pore size distribution shows that the mesopores formed by the accumulation have a pore size of 2~20 nm (e.g. Figure 3 (As shown).

[0089] NH3-TPD showed a strong acid desorption peak at 531℃, accounting for 18% of the area (e.g. Figure 4 (As shown).

[0090] The R-space plot shows a Co-Ce coordination peak at 2.40–2.50 Å and no Co-Co coordination peak at 2.10–2.20 Å, proving that cobalt exists in an atomically dispersed form (e.g., Figure 5 As shown in the figure), the fitting results showed that the coordination number of the Co-O bond was 4.4~4.8 and the bond length of the Co-O bond was 1.90~1.96 Å.

[0091] Co 2p XPS: Fitting Co 2+ / Co 3+ The atomic ratio is 2.26 (e.g.) Figure 6 (As shown); Ce 3d XPS: Fitted Ce 3+ / Ce 4+ The atomic ratio is 0.53 (e.g.) Figure 7 As shown); O 1s XPS: Fitted to O ads / O latt The atomic ratio is 2.79 (e.g.) Figure 9 (As shown).

[0092] Based on the above characterization and free radical capture experiments, it is evident that in the Co / s-CeO2 catalyst of this invention, Co is embedded in the CeO2 lattice in single-atom form, forming a unique Co-O-Ce coordination structure. This structure can efficiently activate molecular oxygen to generate superoxide radicals (rather than hydroxyl radicals), thereby selectively catalyzing the oxidation of ethylbenzene to acetophenone. The extremely high reaction rate (9.1 × 10⁻⁻⁻⁶) in Example 1 demonstrates this. 7 mol·m⁻ 2 ·s⁻ 1 The excellent conversion / selectivity are a result of this atomically dispersed Co-O-Ce synergy.

[0093] III. Comparison of carriers with different morphologies

[0094] Following the same method as in Example 1, Co-doped catalysts were prepared using cubic CeO2 (c-CeO2), particulate CeO2 (p-CeO2), and spindle-shaped CeO2 (f-CeO2) as supports. Under the reaction conditions of Example 1, the ethylbenzene conversion rates of Co / c-CeO2, Co / p-CeO2, and Co / f-CeO2 were 42.3%, 59.8%, and 50.3%, respectively, all lower than the 67.9% of Co / s-CeO2. Their reaction rates per unit area were 3.0 × 10⁻⁻⁻⁻⁶. 7 8.6×10⁻ 7 6.2×10⁻ 7 mol·m⁻ 2 ·s⁻ 1 All are lower than 9.1×10⁻ for Co / s-CeO₂. 7It is proven that a spherical morphology is the optimal morphology for achieving atomic-level dispersion.

[0095] IV. Cyclic Stability Test

[0096] The catalyst from Example 1 was centrifuged, washed three times with anhydrous ethanol, and dried under vacuum at 80°C for 24 h before being used directly in the next reaction. The reaction conditions were the same as in Example 1. The results of five cycles are shown in Table 2.

[0097] 1st time 67.9 88.3 2nd time 67.8 88.2 3rd 67.7 88.1 4th 67.6 88.1 5th 67.6 88.0

[0098] like Figure 12 As shown, the reaction rate did not decrease significantly after 5 cycles; Figure 13 The morphology of Co / s-CeO2 after 5 cycles showed almost no change. Figure 14 The crystal structure remains cubic fluorite; XPS shows that Co after cycling... 2+ / Co 3+ The atomic ratio is 2.26 (e.g.) Figure 15 (as shown), Ce 3+ / Ce 4+ The atomic ratio is 0.53 (e.g.) Figure 16 (as shown), O ads / O latt The atomic ratio is 2.79 (e.g.) Figure 17 As shown in the figure, it is essentially the same as the fresh catalyst. The results indicate that the catalyst of this invention exhibits excellent cycle stability.

[0099] V. Preferred Implementation Methods

[0100] Considering the ethylbenzene conversion, acetophenone selectivity, and reaction rate, Example 1 (cobalt loading 5.0 wt%, reaction temperature 130℃, oxygen pressure 0.6 MPa, reaction time 5 h, using a slow dropwise addition of sodium borohydride without aging) exhibits the best overall performance (conversion rate 67.9%, selectivity 88.3%, reaction rate per unit area 9.1 × 10⁻⁻⁻⁶). 7 mol·m⁻ 2 ·s⁻ 1 Furthermore, characterization confirmed that atomic-level dispersion of cobalt was achieved. Therefore, Example 1 is a preferred embodiment of the present invention.

[0101] Based on this, the scope of protection of the present invention is not limited to the specific values ​​mentioned above. Preferably, the mass percentage of cobalt is 2.5~10 wt%, more preferably 3~6 wt%, and most preferably 4.5~5.5 wt%; the ethylbenzene oxidation reaction temperature is preferably 120~140℃, more preferably 125~135℃; the oxygen pressure is preferably 0.4~0.8 MPa, more preferably 0.5~0.7 MPa; and the reaction time is preferably 3~8 h. Conventional adjustments made to the above parameters by those skilled in the art, as long as they do not disrupt the atomically dispersed Co-O-Ce coordination structure, fall within the scope of protection of the present invention.

Claims

1. A cobalt-doped spherical cerium dioxide catalyst, characterized in that, Cobalt atoms are dispersed in the cerium dioxide lattice in single-atom form, forming an oxygen-bridged Co-O-Ce interface structure; the cerium dioxide support is a nanosphere morphology composed of nanoparticles with a particle size of 10-20 nm, and its BET specific surface area is 30-35 m². 2 / g, and the mesopores formed by the accumulation have a diameter of 2~20nm.

2. The cobalt-doped spherical cerium dioxide catalyst according to claim 1, characterized in that, Co on the surface of cobalt-doped spherical cerium dioxide catalyst 2+ / Co 3+ The atomic ratio is 2.2~2.3, Ce 3+ / Ce 4+ With an atomic ratio of 0.50~0.55, the surface adsorbed oxygen and lattice oxygen are O ads / O latt The atomic ratio is 2.7~2.

8.

3. The cobalt-doped spherical cerium dioxide catalyst according to claim 1, characterized in that, In the XRD pattern of the cobalt-doped spherical cerium dioxide catalyst, the (111) crystal plane diffraction peak of CeO2 is shifted at a higher angle by ≥0.25° relative to pure spherical CeO2, and the lattice shrinkage rate is ≥0.8%.

4. The cobalt-doped spherical cerium dioxide catalyst according to claim 1, characterized in that, In the Co K-edge EXAFS spectrum of the catalyst, there is a Co-Ce coordination peak at 2.40~2.50 Å, and no Co-Co coordination peak at 2.10~2.20 Å; the Co-O bond coordination number is 4.4~4.8, and the Co-O bond length is 1.90~1.96 Å.

5. The cobalt-doped spherical cerium dioxide catalyst according to claim 1, characterized in that, The cobalt content is 3-6 wt%.

6. The cobalt-doped spherical cerium dioxide catalyst according to claim 1, characterized in that, In the NH3-TPD spectrum of the catalyst, there is a strong acid desorption peak in the range of 500~550℃, and its area accounts for ≥15% of the total desorption peak area.

7. A method for preparing the cobalt-doped spherical cerium dioxide catalyst according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Dissolve cerium salt in water, add alkaline solution, and after aging, hydrothermal treatment, washing, drying and calcination, s-CeO2 with nanosphere morphology is obtained; wherein, the hydrothermal temperature is 120~130℃, and the alkaline solution used is sodium hydroxide solution with a concentration of 5~7mol / L; (2) The s-CeO2 support with nanosphere morphology obtained in step (1) is dispersed with cobalt salt in deionized water and stirred for 1-2 hours to obtain mixture A; the cobalt salt is cobalt nitrate, and the theoretical doping amount of cobalt is 3-6 wt%; (3) Dissolve sodium borohydride in deionized water to obtain solution B; (4) Add solution B dropwise to mixture A at a rate of 0.5~1.0 mL / min while stirring, and react at room temperature for 1~3 hours. Centrifuge within 10 minutes after the reaction is completed. (5) Centrifuge to separate the solid, wash it with deionized water and anhydrous ethanol alternately 3 to 5 times, and then dry it under vacuum to obtain cobalt-doped spherical cerium dioxide catalyst.

8. The application of the cobalt-doped spherical cerium dioxide catalyst according to any one of claims 1-7 in the selective oxidation of ethylbenzene to acetophenone under solvent-free and free radical initiator-free conditions.

9. The application according to claim 8, characterized in that, Cobalt-doped spherical cerium dioxide catalyst and ethylbenzene were added to a high-pressure reactor, and oxygen was introduced to a pressure of 0.5~0.7 MPa. The reactor was stirred and reacted at 120~140℃ for 3~6 hours. The mass ratio of cobalt-doped spherical cerium dioxide catalyst to ethylbenzene was 1:40~1:

60. After the reaction was completed, the cobalt-doped spherical cerium dioxide catalyst was separated by centrifugation to obtain a product mixture containing acetophenone.

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