Attapulgite supported cobalt catalyst, method of making and use in olefin epoxidation

Abstract

This invention relates to a cobalt-supported pachytite catalyst, its preparation method, and its application in olefin epoxidation. The method includes the following steps: pre-treated pachytite is acidified with an organic acid to obtain acidified pachytite; the acidified pachytite and a cobalt source are added to water, and a hydrothermal reaction is carried out under stirring conditions; after the reaction, post-treatment is performed, and the pachytite-supported cobalt catalyst is collected. This invention uses organic acid to treat pachytite, which helps increase the interlayer spacing of the pachytite, thereby enabling the loading of metallic cobalt and providing a favorable catalytic environment for promoting the styrene epoxidation reaction. The catalyst obtained by this invention can be recycled for olefin epoxidation, significantly increasing the conversion and selectivity of olefins and effectively reducing byproducts. Under the action of this catalyst, oxygen from the air or directly introduced oxygen can be used as the oxidant, effectively reducing costs, avoiding pollution, and preventing the introduction of other impurities, which is beneficial for product separation and results in high purity.

Description

Technical Field

[0001] This invention relates to the field of catalysts, specifically to attapulgite-supported cobalt catalysts, their preparation methods, and their application in olefin epoxidation. Background Technology

[0002] Epoxides can be prepared by oxidizing olefins with oxidants, and epoxide products play a very important role in medicinal chemistry and fine chemistry. For example, ethylene oxide, obtained from the epoxidation of styrene, is an intermediate in the synthesis of fragrances and pharmaceuticals and is commonly used as an absorbent in epoxy resins and ultraviolet light. Other epoxides are used in pharmaceuticals, perfumes, sweeteners, etc. However, the epoxidation process of styrene remains relatively difficult because it can be further oxidized to benzoic acid or benzaldehyde in the presence of oxidants. Styrene oxidation is industrially prepared directly via the haloalcohol process, which is environmentally harmful and highly corrosive due to the addition of strong oxidants such as H2O2. Therefore, it is necessary to develop environmentally friendly and recyclable systems. The epoxidation process of styrene requires specific active sites, and the development of acidic sites in catalysts is particularly important. Yuan Kai et al. demonstrated that this method can effectively improve the conversion rate of methanol to olefins by adjusting the spatial position of the acidic active sites of the zeolite catalyst ZSM-11. Zhang Lihong et al. prepared a zirconium sulfate-doped titanium nitrate nanosheet solid catalyst and found that the Lewis acidic sites generated on the nanosheets can significantly improve catalytic performance. Wang Yang et al. prepared monodisperse hollow carbon / silica spheres (HS / C-SO3H) with primary mesoporous structures using polystyrene as a template. As a solid acid catalyst with a well-developed hollow structure, HS / C-SO3H exhibited excellent catalytic performance in the esterification reaction of oleic acid and methanol.

[0003] The concentration of different acids directly affects the catalytic process. PSLamoureux et al., using the hydrogen electrode reaction (HER / HOR) on a metal catalyst as an example, calculated the reaction process using the applied density function and found that as the pH value increases, the proton donor changes from hydrogen ions to water, and the inherent barrier of water splitting is more significant than that of hydrogen ions. This is the reason why the kinetics of HER are slower in alkaline media than in acidic media. Li Baitao et al. prepared copper-doped mesoporous KIT-6 by adjusting the pH value and studied the heterogeneous oxidative cracking of styrene catalyzed by copper. They found that the structure and morphology of the catalyst changed with pH value. At a pH value of 3.78, about 4.6 wt% Cu(II) successfully bound to the initial KIT-6 framework. Cu-KIT-6 exhibited high catalytic activity and good stability at a pH value of 3.78. At a pH value of 3.78, the conversion and selectivity of Cu-doped Cu-KIT-6 reached 43.5% and 86.6%, respectively. In addition, the pore size of the catalyst material directly affects the catalytic activity of the active metal and influences the catalytic active sites. Yong Jin et al. synthesized S-containing organic-inorganic hybrid mesoporous silica for catalysis of styrene. The results showed that the conversion and selectivity of styrene reached 50.4% and 92.1%, respectively. Many methods exist for the epoxidation of olefins to prepare epoxides, but most suffer from drawbacks such as numerous byproducts, high oxidant prices, and environmental pollution, limiting the epoxidation process of olefins and negatively impacting industrial development. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a tropane-supported cobalt catalyst, its preparation method, and its application in olefin epoxidation, thereby solving the technical problems of numerous by-products, high oxidant prices, and significant pollution in the preparation of epoxides from olefin epoxidation in the prior art.

[0005] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a cobalt catalyst supported on retardite, comprising the following steps: acidifying retardite that has undergone impurity removal pretreatment with an organic acid to obtain acidified retardite; adding the acidified retardite and a cobalt source to water and carrying out a hydrothermal reaction under stirring conditions; performing post-treatment after the reaction is completed and collecting the cobalt catalyst supported on retardite.

[0007] Preferably, the attapulgite is sodium-type attapulgite; the impurity removal pretreatment involves placing the attapulgite raw material in water and stirring it into a suspension, then letting it stand for more than 20 hours to remove the upper liquid, repeating this process 2 to 4 times, and then drying it.

[0008] Preferably, the organic acid includes tartaric acid. Tartaric acid is a low molecular weight organic acid that can provide more solid acid active sites in attapulgite and provide better reaction sites for the catalytic epoxidation of styrene.

[0009] Preferably, during acidification, the ratio of attapulgite to organic acid is 1 g: (3-8) mL; the concentration of organic acid is 0.01 mmol / L to 0.15 mmol / L. More preferably, the concentration of organic acid is 0.01 mmol / L to 0.10 mmol / L.

[0010] Preferably, during the acidification treatment, attapulgite is first soaked and stirred in an organic acid for 4–8 hours, then centrifuged, washed, and dried to obtain acidified attapulgite. More preferably, the drying is performed by baking at 80–120°C for 10–14 hours.

[0011] Preferably, the cobalt source is Co(NO3)2·6H2O or Co(CH3COO)2·4H2O, with Co(CH3COO)2·4H2O being the most preferred.

[0012] Preferably, the ratio between acidified retardite and cobalt source is 0.5 g: (0.3–5) mmol.

[0013] Preferably, during the hydrothermal reaction, the ratio of acidified attapulgite to added water is 0.5 g: (20-40) mL.

[0014] Preferably, the hydrothermal reaction is carried out at 80–100°C for more than 5 hours.

[0015] Secondly, the present invention provides a rettostel-supported cobalt catalyst prepared by the above preparation methods.

[0016] Thirdly, the present invention provides an application of the above-mentioned attapulgite-supported cobalt catalyst in the catalytic epoxidation of olefins.

[0017] Preferably, the olefin epoxidation reaction specifically includes: mixing olefin, TBHP, solvent and attapulgite-supported cobalt catalyst to form a reaction solution, introducing air or oxygen into the reaction solution, heating the reaction, and centrifuging to remove the supernatant after the reaction is completed to obtain the olefin epoxidation product.

[0018] More preferably, the ratio of olefin, TBHP and attapulgite-supported cobalt catalyst is 3 mmol: (0.1–0.5) mmol: (80–120) mg.

[0019] More preferably, the ratio of olefin to solvent is 3 mmol: (8–12) g.

[0020] More preferably, the heating reaction is carried out at 70–110°C for 3–8 hours.

[0021] More preferably, the rate of air or oxygen flow is 35–45 mL / min.

[0022] Compared with the prior art, the beneficial effects of the present invention include:

[0023] This invention utilizes organic acid treatment to increase the interlayer spacing of attapulgite, thereby enabling the loading of cobalt metal and providing a favorable catalytic environment for the epoxidation of styrene. The catalyst obtained by this invention, when used in the efficient air epoxidation of olefins, exhibits a co-catalytic effect between the organic acid and the supported cobalt, working synergistically with the attapulgite support to significantly increase the conversion and selectivity of olefins while effectively reducing byproducts. Furthermore, this catalyst is recyclable. Simultaneously, under the action of this catalyst, oxygen from the air or directly introduced oxygen can be used as the oxidant for olefin epoxidation, effectively reducing costs, avoiding pollution, and preventing the introduction of other impurities, thus facilitating product separation and achieving high purity. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the synthesis process of the present invention;

[0025] Figure 2 These are the test spectra of the present invention; wherein (a) is the XRD spectrum of H(x)-Na(Co)-Rec and TA(x)-Na(Co)-Rec, (b) is the IR spectrum of H(x)-Na(Co)-Rec and TA(x)-Na(Co)-Rec, (c) is the XPS spectrum of Co 2p, and (d) is the XPS spectrum of C1s.

[0026] Figure 3 These are scanning electron microscope (SEM) images of the products obtained in this invention; where (a) and (b) are SEM images of Na-Rec; (c) and (d) are SEM images of Co-Rec (cobalt content is 3%); (e) and (f) are SEM images of H-Co-Rec; (the acidification concentration of TA is 0.1 mmol / L).

[0027] Figure 4 This is a surface acidity diagram of Na-Rec, Co-Rec, and H-Co-Rec tested by NH3-TPD.

[0028] Figure 5 This is a schematic diagram of the air epoxidation reaction of styrene and α-pinene according to the present invention.

[0029] Figure 6 The effects of different synthesis conditions on styrene conversion of catalysts are as follows: (a) different types of acids; (b) different active metals; (c) different cobalt contents; (d) different supports.

[0030] Reaction conditions: Styrene: 3 mmol; Catalyst: 100 mg; TBHP: 0.3 mmol; Time: 5 h; Temperature: 90 °C; DMF: 10 g; Air flow rate: 40 mL / min

[0031] Figure 7 The effect of different catalyst synthesis methods on the epoxidation reaction of styrene was investigated. Reaction conditions: olefin 3 mmol; catalyst 100 mg; TBHP 0.3 mmol; time: 5 h; temperature: 90 °C; DMF 10 g; air flow rate 40 mL / min.

[0032] Figure 8 This is a schematic diagram of the mechanism of olefin epoxidation reaction, taking α-pinene as an example. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Pitotite is an interlayered clay mineral, mainly distributed in Zhongxiang, Hubei Province. It is an interlayered mineral composed of a 2:1 ratio of mica and montmorillonite layers, thus possessing both the high-temperature resistance of mica and the ion-exchange properties of montmorillonite. The unique interlayered structure of pitotite significantly enhances its ion-exchange performance, leading to increased research in recent years. For example, iron-modified pitotite exhibits good adsorption and visible light photocatalytic properties, and pitotite can be modified with carbon layers and trisodium trimetaphosphate to remove Pb. 2+ Because of the presence of heavy metal ions, current research on attapulgite mainly focuses on degradation and photocatalytic materials, while there are few reports on molecular oxygen catalysis.

[0035] This invention uses sodium retarder as a raw material, obtained through washing and cold drying to screen for finer sodium retarder particles. The obtained sodium retarder is then modified with different acids to serve as a support for loading the active metal Co. This material is then applied to the catalytic epoxidation of styrene. It was found that tartaric acid acidification and loading of trace amounts of active metal Co on sodium retarder (Na-Rec) significantly increased the conversion and selectivity of styrene. Furthermore, the performance did not significantly decrease after four cycles, further demonstrating that organic acids can provide more solid acid active sites in retarder and offer better reaction sites for the catalytic epoxidation of styrene.

[0036] The present invention will be further described in detail below through specific embodiments and comparative examples.

[0037] The materials used in this invention include Co(Ac)₂·4H₂O (≥99.0%, Aladdin), Fe(NO₃)₃·9H₂O, Mn(Ac)₂·4H₂O, Zn(Ac)₂·2H₂O, Cu(NO₃)₂·3H₂O, Cr(NO₃)₃·9H₂O, SnCl₂·2H₂O (≥99%, Sinopharm Group), 2,2-dimethylolpropionic acid (DMPA), dimethylolbutyric acid (DMBA) (≥99.0%, Aladdin), TBHP (tert-butyl hydroperoxide, ≥65%, Sinopharm Group), α-pinene (≥98.0%, Aladdin), and α-epoxypinene. (≥95%, Sinopharm Group), Styrene (≥98.5%, Sinopharm Group), Limonene (≥95%, Aladdin), 1-Octenene (≥95%, Aladdin), Cyclooctene (≥95%, Aladdin), Methylstyrene (≥99%, Aladdin), DMF (N,N-dimethylformamide, ≥99.5%, Sinopharm Group), Pitotite (Hubei Elite); Nitric acid, Sulfuric acid, Hydrochloric acid (≥99%, Sinopharm Group); Tartaric acid (≥99.0%, Aladdin); Na-Rec (Sodium Pitotite, from Hubei Mingliu), all other chemicals were purchased from the market and did not require further purification.

[0038] Example 1

[0039] 1. Pretreatment of Na-Rec

[0040] To obtain pure rettolith, 5 g of rettolith was placed in a 1 L beaker and stirred at room temperature for 6 hours until a suspension was formed. The rettolith was then pretreated with water. After standing for 24 hours, the colloidal solution at the top was removed by pipette. The above steps were repeated 3 times, and the rettolith was collected by freeze-drying to obtain sodium rettolith (Na-Rec).

[0041] 2. Synthesis of H-Na-Rec

[0042] Add 1 g Na-Rec and 5 mL of 0.1 mmol / L TA (tartaric acid) to a three-necked flask, stir for 6 hours at room temperature, centrifuge, wash 3 times with hot distilled water, centrifuge again to collect the solid, and bake at 100 °C for 12 hours to obtain acidified attapulgite H-Na-Rec.

[0043] 3. Synthesis of H-Co-Rec

[0044] 0.5 g H-Na-Rec, 3 mmol Co(Ac)2·4H2O and 30 mL of water were placed in a flask and stirred overnight at 90 °C. The solid was dried and collected, then ground and sieved. The resulting solid powder was named H-Co-Rec(TA(0.1 mmol / L)).

[0045] Comparative Example 1

[0046] Na-Rec, the starting material, is used directly as the catalyst.

[0047] Comparative Example 2

[0048] The only difference from Example 1 is that the acid treatment in step 2 was omitted, and the acid-free blank test of the prepared Co-Rec was performed. All other steps and conditions were the same as in Example 1; the synthesis process is as follows: Figure 1 As shown, it is similar to the third step in Example 1, but the carrier is Na-Rec, and the subsequent steps are the same.

[0049] Comparative Example 3

[0050] The only difference from Example 1 is that step 3, the cobalt loading treatment, is omitted; the other steps and conditions are the same as in Example 1. TA (0.1 mmol / L)-Na-Rec is prepared.

[0051] Comparative Example 4

[0052] The only difference from Comparative Example 3 is that TA was replaced with HAc (acetic acid), and the other steps and conditions were the same as those in Comparative Example 3; HAc (0.1 mmol / L)-Na-Rec was prepared.

[0053] Comparative Example 5

[0054] The only difference from Comparative Example 3 is that the TA concentration was adjusted to 0.5 mmol / L, 1.0 mmol / L, and 2.0 mmol / L, while the other steps and conditions were the same as those in Comparative Example 3; TA(0.5 mmol / L)-Na-Rec, TA(1.0 ​​mmol / L)-Na-Rec and TA(2.0 mmol / L)-Na-Rec were prepared respectively.

[0055] Performance testing

[0056] Using a Rigaku, MiniFlex 600X-650 diffractometer, Cu Kα radiation was employed. Samples were tested by X-ray diffraction (XRD) at a scan rate of 1° / min in the range of 2-50° (30-40kV, 25mA).

[0057] Scanning electron microscopy (SEM) images were obtained on a JEOL (JSM6700 F) with an accelerating voltage of 15 kV.

[0058] FTIR (Fourier Transform Infrared) spectroscopy was performed on a Thermofisher Nicolet IS5 Fourier Transform Infrared Spectrophotometer, ranging from 400 to 4000 cm⁻¹. -1 .

[0059] TEM (transmission electron microscopy) images were obtained using a JEOL-135 2010F transmission electron microscope at an accelerating voltage of 200 kV.

[0060] X-ray photoelectron spectroscopy (XPS) was recorded on the Perkin Elmer PHI ESCA system.

[0061] The NH3 temperature-programmed desorption (NH3-TPD) analysis results of the material were tested using an automated gas adsorption analyzer (TP-5076).

[0062] In this invention, a catalyst was prepared via hydrothermal synthesis utilizing the ion exchange properties of the support itself. The morphological changes of attapulgite after acid modification and after loading with an active metal were compared using XRD and IR spectroscopy, such as... Figure 2 As shown in ab.

[0063] For ease of comparison, the H-Co-Rec obtained in Example 1 is represented as TA(0.1mmol / L)-Co-Rec; from Figure 2 As shown in Figure a, after acidification with 0.1 mmol / L HAc (acetic acid) in Comparative Example 4 and with TA (tartaric acid) in Comparative Example 3, the 2θ of attapulgite changed from 3.96 (Comparative Example 1) to 3.76 (HAc(0.1 mmol / L)-Na-Rec) and 3.30 (TA(0.1 mmol / L)-Na-Rec), respectively. The Bragg equation shows that the interlayer spacing expanded from 2.2315 to 2.3502 and 2.6776, indicating that acidification is beneficial for increasing the interlayer spacing of attapulgite. To further investigate the effect of acidification concentration on the interlayer spacing of attapulgite, the acidification concentration was changed without the addition of active metal cobalt (Comparative Example 5). It was found that the tartaric acid concentration of 0.1 mmol / L had the greatest effect on the interlayer spacing of attapulgite, with a significantly higher and narrower peak at 2θ = 3.96 compared to Na-Rec. This is because the acidified attapulgite layers have good crystallinity, and some tartaric acid ions may insert into the interlayer spaces of the attapulgite, leading to an increase in the interlayer spacing of the material. Meanwhile, the changes in interlayer spacing of attapulgite after loading with the active metal Co were compared. It was found that the interlayer spacing continued to increase, but not significantly, while the intensity of the characteristic diffraction peaks decreased markedly. This may be because Co... 2+ It can penetrate the mica layer and interact with the Na in the montmorillonite layer. + The exchange resulted in a decrease in the intensity of the diffraction peaks. However, the overall matrix of rettosite did not change significantly.

[0064] like Figure 2 Figure b shows the infrared spectra of H(x)-Na(Co)-Rec and TA(x)-Na(Co)-Rec. In the FT-IR spectrum, 3653 cm⁻¹... -1 and 1678cm -1The peak at 1080 cm⁻¹ corresponds to the stretching peak of the hydroxyl groups in the hydrogen-bonded Si-O-Si layer and the bending vibration peak of the H-OH bonds in the interlayer water layer. -1 The peak value belongs to the asymmetric tensile vibration of the Si-O-Si bond with asymmetric tensile vibration, and 573 cm⁻¹ -1 The peak is attributed to the asymmetric tensile vibration of the Si-O-Si bond. Due to the tensile vibration of Al-O-Si, the peak at 492 cm⁻¹... -1 The peak value indicates the bending vibration of the Si-O bond. It can be concluded that the characteristic absorption peak of attapulgite does not change during the acidification displacement, therefore the interlayer structure of attapulgite also remains unchanged, a conclusion consistent with XRD.

[0065] X-ray photoelectron spectroscopy (XPS) was used to further investigate the composition and chemical morphology of the H-Co-Rec surface. To analyze the valence state of Co in rettosite, the XPS spectrum of Co2p was fitted, as shown below. Figure 2 As shown in cd, Co was observed at 785.28 eV and 801.98 eV. 2+ The oxidation state of the oxygen is represented by satellite peaks caused by low-intensity vibrations at 785.28 eV and 801.98 eV. These satellite peaks are due to the low-spin Co... 3+ Cations can only produce higher spin Co 2+ Weak satellite peaks. The peak values ​​for Co 2p3 / 2 and Co 2p1 / 2 are 780.58 eV and 796.18 eV, respectively, indicating that metallic Co exists as a secondary component in attapulgite, which is consistent with literature reports. Furthermore, Co in attapulgite... 2+ Ion exchange with Na + Acidification does not affect the valence state of the metal.

[0066] SEM images were used to explore the surface morphology of Na-Rec (Comparative Example 1), Co-Rec (Comparative Example 2), and H-Co-Rec (0.1 mmol / L). Figure 3 As shown, Figure 3 ab shows Na-Rec at different scales and indicates that when the magnification is 200 nm, as Figure 3 As shown in b, the layers of rettosite are tightly connected, and the mica structure can be observed very clearly. Figure 3 The CD diagram shows the morphology of Co-Rec. From these figures, it can be seen that after loading the active metal Co between the recalcitrant layers using a hydrothermal exchange method, the structure of the recalcitrant layers remained unchanged, but the interlayer spacing changed; however, after acidification with tartaric acid and loading cobalt (Example 1), as... Figure 3 As shown in ef, the interlayer spacing of the difficult-to-decompose layers changed significantly, compared with... Figure 3Compared to 3a, the interlayer spacing in d is significantly larger. The above figure further confirms that tartaric acid can regulate the interlayer spacing of attapulgite, providing a favorable environment for promoting the epoxidation reaction of styrene. This conclusion is consistent with the XRD results.

[0067] The acidity of the catalyst surfaces of Comparative Example 1 (Na-Rec), Comparative Example 2 (Co-Rec), and Example 1 (H-Co-Rec) was determined by NH3-TPD analysis. Figure 4 As can be seen from the data, a strong and broad peak in Na-Rec at 400-675℃ indicates the adsorption of H3O by tetrahedral AlO4. + It is a weakly acidic center, which transforms into Si-O(H)-Al after dehydration and exhibits strong acidity. The weaker peaks of Co-Rec at 200-400℃ and 400-675℃ indicate that Co... 2+ Na in montmorillonite layers + Exchange. In comparison, Co-Rec exhibits a lower desorption temperature and generally weaker acidity, which contributes to improved catalytic activity. H-Co-Rec shows weak peaks at 150-275℃, 275-450℃, and 450-600℃. The peak at 150-275℃ is caused by the -OH group on the TA. 2+ In the presence of [a specific substance], the acidity of the Na-Rec surface is further reduced, and the catalytic activity is improved.

[0068] Application Example 1

[0069] The epoxidation reaction of olefins at atmospheric pressure was carried out in a three-necked flask equipped with a reflux condenser. Specifically, 3 mmol of styrene, 0.3 mmol of TBHP, 10 g of DMF, and 100 mg or more of the catalyst obtained in Example 1 were added to the three-necked flask, and the mixture was rapidly stirred with a magnetic stirrer and then placed in an oil bath at 90 °C. Air at a flow rate of 40 mmol / min was introduced into the bottom of the reactor through a gas generator to initiate the reaction. After the reaction was complete, the supernatant was removed by centrifugation, and the mixture was analyzed on a Trace 1300GC analyzer equipped with an FID detector and a capillary column (Rtx@-5, 30 m x 0.25 mm x 0.25 μm), using chlorobenzene as an internal standard.

[0070] Comparative Example 6

[0071] The only difference from Example 1 is that the type of acid replaced in step 2 is nitric acid, hydrochloric acid, nitric acid:hydrochloric acid = 1:1, citric acid or PTA (terephthalic acid) and other organic acids. The other steps and conditions are the same as in Example 1. The catalyst is prepared as shown in Table 1 below.

[0072] Application Comparative Example 1

[0073] The only difference from Application Example 1 is that the catalyst obtained in Comparative Example 1 (acid-free treatment) or Comparative Example 6 is used instead of the catalyst obtained in Example 1, while the other steps and conditions are the same as in Application Example 1.

[0074] The catalytic activity of H-Co-Rec was studied by the epoxidation of styrene under air conditions, such as... Figure 5 As shown. The main product in the epoxidation of styrene is the epoxidation product, and byproducts also include benzaldehyde and phenylacetaldehyde.

[0075] This invention investigated the effects of low molecular weight organic acids (LMWOAs) and various inorganic acids at the same concentration on the catalytic epoxidation of olefins, such as... Figure 6 As shown in Figure a, tartaric acid (TA) acidification of retardant significantly improved the conversion rate of styrene. Compared with the Co-Rec catalyst in Comparative Example 1, the presence of tartaric acid increased the conversion rate of styrene from 70.25 mol% to 95.20 mol%, although the selectivity decreased slightly (from 90.11% to 88.67%), the yield of styrene was significantly improved. While the catalysts in Comparative Example 6 treated with hydrochloric acid, sulfuric acid, and nitric acid showed catalytic activity for styrene, their selectivity for epoxide products was much lower. By comparing the catalytic effects of other organic acids under the same conditions, it was found that PTA, acetic acid, DMPA, and DMBA did not have a higher catalytic activity for olefins than tartaric acid, and their conversion rates were also lower than those of tartaric acid. Specific results are shown in Table 1 below.

[0076] Table 1. Results of catalyst application under different acid treatments

[0077] catalyst Types of acids Styrene conversion rate (mol%) Selectivity (%) Co-Rec / 70.25 90.11 H-Co-Rec(TA(0.1mmol / L)) tartaric acid 95.20 88.67 <![CDATA[H2SO4-Co-Rec]]> sulfuric acid 52.9 66.9 HCl-Co-Rec hydrochloric acid 71.3 49.6 <![CDATA[HNO3-Co-Rec]]> Nitric acid 40.8 55.4 PTA-Co-Rec terephthalic acid 32.0 84.9 HAc-Co-Rec Acetic acid 31.4 62.7 DMPA-Co-Rec 2,2-Dimethylolpropionic acid 41.2 81.97 DMBA-Co-Rec 2,2-Dihydroxymethylbutyric acid 26.04 75.5

[0078] This further demonstrates that TA itself is important for the activation of molecular oxygen.

[0079] Comparative Example 7

[0080] The only difference from Example 1 is that the metal loaded in step 3 is replaced with Cr, Fe, Sn, Cu or Mn (the specific raw materials are as described above), or Co(NO3)2·6H2O is used as the source; the other steps and conditions are the same as in Example 1, and the catalyst is obtained.

[0081] Application Comparative Example 2

[0082] The only difference from Application Example 1 is that the catalyst obtained in Comparative Example 7 is used for the epoxidation of styrene, while the other steps and conditions are the same as in Application Example 1.

[0083] To demonstrate that Co exhibits superior catalytic activity towards styrene compared to other reactive metals, Cr, Fe, Sn, and Mn were used as comparative experiments. The results are as follows: Figure 6 As shown in b.

[0084] For styrene, metallic Mn and metallic Cr are more catalytic than Sn and Fe, with molar conversions of 48.66 mol% and 67.93 mol% for 3 mmol styrene, respectively, and selectivities for epoxidation products of 83.94% and 79.35%, respectively, while the conversions of H-Sn-Rec and H-Fe-Rec are only 18.06 mol% and 26.74 mol%, respectively.

[0085] The effects of different Co sources on the catalytic epoxidation of styrene were compared. Using H-Co(NO3)2·6H2O-Rec and H-Co(CH3COO)2·4H2O-Rec as catalysts, it was found that their catalytic effects on styrene were quite different, with styrene conversion rates of 68.82 mol% and 95.20 mol%, respectively. This indicates that in the presence of low molecular weight organic acids, using Co(CH3COO)2·4H2O as a cobalt source is more conducive to attapulgite-loaded cobalt metal.

[0086] Comparative Example 8

[0087] The only difference from Example 1 is that the cobalt content loaded in step 3 is adjusted to 1 mmol, 5 mmol, 7 mmol, 10 mmol or 15 mmol; the other steps and conditions are the same as in Example 1, and the catalyst is obtained.

[0088] Application Comparative Example 3

[0089] The only difference from Application Example 1 is that the catalyst obtained from Comparative Example 8 is used for the epoxidation of styrene, while the other steps and conditions are the same as in Application Example 1.

[0090] The content of the active metal Co further affects the yield of styrene epoxidation, such as... Figure 6 As shown in Figure c, for 3 mmol styrene, when the Co content is 1 mmol, the styrene conversion rate is less than 20 mol%. As the Co content increases, the styrene conversion rate increases to 95.20 mol%, and the selectivity of the epoxide is greater than 85%. When the Co content continues to increase, the styrene conversion rate is less than 80 mol%, and the selectivity of the epoxide product further decreases, indicating that excessive cobalt content is not conducive to the epoxidation reaction of styrene. Therefore, the optimal cobalt content is selected as 3 mmol.

[0091] Comparative Example 9

[0092] The only difference from Example 1 is that the attapulgite support is replaced with SiO2, ZSM-5 molecular sieve, MOR molecular sieve, X-type molecular sieve, β-type molecular sieve or Y-type molecular sieve, respectively; the other steps and conditions are the same as in Example 1, and the catalyst is obtained.

[0093] Application Comparative Example 4

[0094] The only difference from Application Example 1 is that the catalyst obtained from Comparative Example 9 is used for the epoxidation of styrene, while the other steps and conditions are the same as in Application Example 1.

[0095] The catalytic activities of H-Co-Rec, H-Co-SiO2, H-Co-ZSM-5, H-Co-MOR, H-Co-X, H-Co-β and H-Co-Y were investigated by epoxidation of styrene with air.

[0096] like Figure 5 As shown, the epoxidation product of styrene is the main product, and byproducts include benzaldehyde and phenylacetaldehyde; from Figure 6 As can be seen from d, H-Co-Rec and H-Co-β have comparable catalytic abilities for styrene, but H-Co-β has a much lower selectivity for epoxidation of styrene. The catalytic activity of styrene using H-Co-ZSM-5 and H-Co-X is very poor. In contrast, the catalytic activity of styrene using H-Co-SiO2, H-Co-MOR, and H-Co-Y materials is relatively poor. This indicates that the reaction sites provided by various supports and the active sites of the supports themselves have different effects on the catalysis of styrene. Catalysts using retardant as a support exhibit superior catalytic performance compared to other supports.

[0097] As can be seen from the above application examples and comparative examples, the present invention uses low molecular weight organic acid treatment, which can produce a synergistic effect with attapulgite and loaded cobalt.

[0098] Application Example 2

[0099] The only difference from Application Example 1 is that different olefins are epoxidized, while the other steps and conditions are the same as in Application Example 1.

[0100] To demonstrate the catalytic ability of H-Co-Rec for other olefins, it was applied to the catalytic epoxidation reaction of other substrates, and the results are shown in Table 2.

[0101] Table 2 Catalytic performance tests of catalysts for different olefins

[0102]

[0103]

[0104] Table 2 shows that H-Co-Rec has a catalytic capacity of 95.20 mol% for styrene and a selectivity of 88.67% for epoxidation products. The catalytic performance for α-pinene and methylstyrene is 88.29 mol% and 83.34 mol%, respectively. The catalytic performance for 1-octene and limonene is the next best, with conversion rates of 53.52 mol% and 54.96 mol%, respectively. The catalytic capacity for cyclooctene is the worst, at only 9.18%, indicating that H-Co-Rec has a good catalytic capacity for olefins.

[0105] Application Example 3

[0106] Based on Example 1 and Application Example 1, the corresponding conditions were adjusted to investigate the effects of different catalyst synthesis methods and different reaction conditions on the styrene epoxidation reaction.

[0107] Reaction conditions: olefin 3 mmol; catalyst 100 mg; TBHP 0.3 mmol; time: 5 h; temperature: 90 °C; DMF 10 g; air flow rate 40 mL / min.

[0108] Figure 7 The effect of low molecular weight organic acid (TA) content on the catalytic activity of the material was investigated.

[0109] For 0.5 g of tartaric acid, when the concentration of TA increased from 0.01 mmol / L to 0.1 mmol / L, the styrene conversion increased from 32.92 mol% to 95.20 mol%, and the selectivity of the epoxide product increased from 70.07% to 88.67%. Furthermore, the styrene conversion significantly decreased with further increases in the TA content, indicating that excessive tartaric acid loading on tartaric acid cannot promote the epoxidation reaction of styrene. Therefore, the present invention preferably uses a low molecular weight organic acid concentration of 0.01 mmol / L to 0.15 mmol / L; among which, 0.1 mmol / L of TA showed the best performance in styrene conversion and epoxide product selectivity within a reasonable time range.

[0110] At the same time, the reaction time was optimized, such as Figure 7 As shown in b, the conversion rate of styrene significantly increases with increasing reaction time. Within a 5-hour reaction period, the styrene conversion rate reaches 95.20 mol%, and the selectivity of the epoxy product reaches 88.67%. Although the styrene conversion rate can continue to increase with further increases in reaction time, the selectivity of the epoxy product only reaches 87.60% within the reaction time. Therefore, the optimal reaction time is 5 hours.

[0111] The cycling performance of H-Co-Rec catalysts is as follows: Figure 7As shown in c, after four cycles of the catalyst, the styrene conversion rate still reached 63.34 mol%, and the selectivity of the epoxy product reached 73.33%. This is because after the tartaric acid material itself is loaded into the interlayer as a hydrophilic substance, the tartaric acid cannot exist stably in the interlayer of the attapulgite, resulting in a decrease in the concentration of tartaric acid in the catalytic system and further reducing the catalytic activity of the catalyst.

[0112] The effects of different synthesis methods on the catalytic activity of the catalyst were compared, such as Figure 7 As shown in Figure d, using H-Na-Rec increased the styrene conversion to 50.3 mol%, while using Na-Rec directly as a catalyst only increased it to 13.2 mol%, further indicating that TA promoted the epoxidation reaction of styrene. 2+ In the case of physical mixing with Na-Rec, with Co 2+ Using a physical mixture of tartaric acid and Co-Rec as a catalyst, the styrene conversion rate was only 18.7 mol%, indicating that the hydrothermal synthesis method is favorable for Co loading in the attapulgite interlayer to achieve catalytic effect. Using a physical mixture of tartaric acid and Co-Rec directly as a catalyst, the styrene conversion rate was only 31.5 mol%, and the catalytic activity was lower than using H-Na-Rec alone as a catalyst. The results further indicate that the hydrothermal synthesis method is favorable for tartaric acid loading in attapulgite, and that tartaric acid and Co... 2+ The synergistic effect is beneficial to the epoxidation of styrene.

[0113] This invention uses α-pinene as an example to illustrate the mechanism of olefin epoxidation reaction:

[0114] The reaction mechanism of this invention is as follows: Figure 8 As shown, and based on the XPS results of retardant, it exists in divalent cobalt and Co. 2+ Na ions + Ion exchange, in the presence of DMF and air, occurs due to the combination of air and TBHP to form DMF-Rec-Co. 3+ The presence of an OO-metal complex leads to the oxidation of the double bond on pinene to a transition state. Simultaneously, with the increase of Co... 3+ To Co 2+ The transformation occurs as excess metal complexes continue to form cyclic peroxide radicals, which react with α-pinene to form epoxide pinane.

[0115] The mechanism of action for styrene is the same. During the epoxidation of styrene, the presence of DMF and TBHP inevitably leads to the formation of a small amount of ·OH, producing byproducts such as benzaldehyde and benzoic acid. In this invention, the generated -OH in the reaction system can compete with low-molecular-weight organic acids, thereby accelerating the epoxidation reaction of olefins. At the same time, the attapulgite is modified with a low-molecular-weight organic acid (such as TA), and the TA between the attapulgite layers is used as a proton solvent to prevent the homopolymerization of H2O2 molecules in TBHP, thereby promoting the epoxidation of styrene.

[0116] This invention prepared a series of cobalt-parotide catalysts using a hydrothermal synthesis method. The catalytic epoxidation of olefins by organic and inorganic acids after tartaric acid treatment of pattarolite was compared. The results showed that the catalyst treated with tartaric acid exhibited a significant catalytic effect on styrene, and different acid concentrations also had a significant impact on the catalytic effect on styrene. Simultaneously, the catalytic epoxidation of olefins by catalysts prepared with different amounts of cobalt and different metals was investigated. The results showed that 0.1 mmol / L tartaric acid and pattarolite treated with supported active metal cobalt exhibited excellent catalytic activity for the epoxidation of styrene.

[0117] In summary, this invention utilizes the unique layered structure of attapulgite to synthesize a supported catalyst, H-Co-Rec, which was found to be highly effective for the epoxidation of styrene. Furthermore, it was discovered that low molecular weight organic acids also exhibit co-catalytic activity in the epoxidation of olefins. XRD and SEM characterization showed that different concentrations of organic acids acting on attapulgite directly increase its interlayer spacing. Under air as the oxidant, when the organic acid concentration was 0.1 mmol / L, the styrene conversion reached 95.20 mol%, and the selectivity of the epoxide product reached 88.67%. This is because the low molecular weight organic acids can compete with -OH radicals, accelerating the conversion of olefins and improving the selectivity of the epoxide product.

[0118] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a attapulgite-supported cobalt catalyst, characterized in that, Includes the following steps: At room temperature, retardant stone that has undergone impurity removal pretreatment is acidified with an organic acid to obtain acidified retardant stone; the organic acid is tartaric acid; during the acidification treatment, the ratio of retardant stone to organic acid is 1 g: (3-8) mL; the concentration of organic acid is 0.1 mmol / L to 0.15 mmol / L. Acidified retardite and cobalt source were added to water and hydrothermal reaction was carried out under stirring. After the reaction was completed, post-processing was performed to collect the retardite-supported cobalt catalyst. During the acidification process, attapulgite is first soaked and stirred in an organic acid for 4–8 hours, then centrifuged, washed, and dried to obtain acidified attapulgite. The cobalt source is Co(CH3COO)2•4H2O; The ratio between acidified rettosite and cobalt source was 0.5 g: (3–5) mmol; The hydrothermal reaction is carried out by heating at 80–100°C for more than 5 hours.

2. The method for preparing the attapulgite-supported cobalt catalyst according to claim 1, characterized in that, The attapulgite is sodium-type attapulgite; the impurity removal pretreatment involves placing the attapulgite raw material in water and stirring it into a suspension, then letting it stand for more than 20 hours to remove the upper liquid, repeating this process 2 to 4 times, and then drying it.

3. The attapulgite-supported cobalt catalyst prepared by the preparation method according to any one of claims 1-2.

4. The application of the rapasite-supported cobalt catalyst as described in claim 3 in the catalytic epoxidation of olefins.

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