A manganese-modified cobalt oxide catalyst and a method for catalyzing selective oxidation of benzyl alcohol

Abstract

The present application relates to the technical field of heterogeneous catalysis, and particularly relates to a manganese-modified cobalt oxide catalyst and a method for catalyzing selective oxidation of benzyl alcohol. In the present application, a very significant catalytic performance enhancement effect can be produced by adding a small amount of manganese to the oxide of cobalt. In selective oxidation of benzyl alcohol using air as an oxidant, 100% conversion of benzyl alcohol can be obtained using the present catalyst, and the selectivity of benzaldehyde is 100%. The air used as an oxidant in the reaction exists in the reactor space above the liquid surface of the reaction mixture in a normal pressure state, and a special pipeline is not required to be introduced into the reactor or the reaction mixture, and the air does not need to be pressurized to be dissolved into the reaction mixture. The pressure in the reactor during the reaction is also maintained at a normal pressure, and the oxygen in the air can enter the reaction liquid by stirring the reaction mixture, so that the benzyl alcohol can be fully reacted with the oxygen to realize high-efficiency selective oxidation of the benzyl alcohol, and the present application has an ideal application prospect.

Description

Technical Field

[0001] This invention relates to the field of heterogeneous catalysis technology, specifically to a manganese-modified cobalt oxide catalyst and a method for selectively oxidizing benzyl alcohol. Background Technology

[0002] The selective oxidation of alcohols to their corresponding carbonyl compounds in organic synthesis is an important functional group reaction with wide applications in basic organic synthesis, fine chemicals, and industrial manufacturing. Benzaldehyde, as an important raw material and intermediate, is widely used in the pharmaceutical, agricultural, synthetic fragrance, and dye industries.

[0003] Traditional industrial benzaldehyde production routes typically use stoichiometric oxidants (such as chromates, permanganates, and hypochlorites) to selectively oxidize benzyl alcohol. However, this process produces other byproducts besides benzaldehyde, and the reaction process is prone to reactor corrosion and environmental pollution. The selective oxidation of benzyl alcohol to produce benzaldehyde offers good economic and environmental benefits, and can produce high-quality benzaldehyde in food, pharmaceutical, and cosmetic grades, thus attracting widespread attention. In research on the selective oxidation of benzyl alcohol to benzaldehyde, the development of efficient, inexpensive, and stable non-precious metal catalysts, as well as efficient catalytic processes based on these catalysts, has always been the core research focus. Summary of the Invention

[0004] This invention aims to provide a method for preparing a manganese-modified cobalt oxide catalyst to address the technical problem of the lack of readily available, inexpensive, simple-to-prepare, and high-performance non-precious metal catalysts in the selective oxidation of benzyl alcohol to benzaldehyde production route. This invention also provides a simple and efficient method for the selective oxidation of benzaldehyde to benzaldehyde based on this catalyst, improving the economic efficiency and environmental friendliness of the production process.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a manganese-modified cobalt oxide catalyst includes the following steps performed sequentially:

[0007] S1: Mix the cobalt precursor and manganese precursor with a solid dispersion medium to obtain a mixture; and the molar ratio of manganese and cobalt elements in the manganese precursor and cobalt precursor is 1:105-1:11;

[0008] S2: Calcination treatment of the mixture to obtain manganese-modified cobalt oxide catalyst Mn-CoOx.

[0009] This technical solution also provides a method for preparing a manganese-modified cobalt oxide catalyst, namely Mn-CoOx.

[0010] This technical solution also provides a method for selective oxidation of benzyl alcohol using the manganese-modified cobalt oxide catalyst Mn-CoOx: benzyl alcohol and manganese-modified cobalt oxide catalyst Mn-CoOx are added to a solvent to obtain a reaction mixture, and air is used as the oxidant to react at 50-91℃ and atmospheric pressure for 5-18 hours to obtain benzaldehyde.

[0011] Furthermore, in S1, the solid dispersion medium is any one of F127, P123, F68, and graphite powder; the cobalt precursor is any one of cobalt nitrate, cobalt acetate, and cobalt oxalate; and the manganese precursor is any one of manganese nitrate, manganese acetate, and manganese oxalate.

[0012] Furthermore, in S2, the calcination temperature is 300-400℃ and the time is 2-4h; and air is introduced during the calcination process.

[0013] Furthermore, the manganese-modified cobalt oxide catalyst Mn-CoOx contains cobalt oxide and manganese elements highly dispersed within the cobalt oxide. XRD analysis of the catalyst obtained in this method revealed only CoCo2O4 species; no manganese oxide species were observed. This is because the amount of manganese used in the employed technique is significantly lower than that of cobalt, resulting in the manganese oxide species being highly dispersed within the CoCo2O4 species during the preparation process.

[0014] Furthermore, air exists at atmospheric pressure in the reactor space above the surface of the reaction mixture; the reactor interior is a closed system, and no air is added during the reaction.

[0015] Furthermore, the solvent is any one of toluene, acetonitrile, and dichloromethane.

[0016] Furthermore, the ratio of benzyl alcohol to manganese-modified cobalt oxide catalyst Mn-CoOx is 0.12-0.24 mL: 0.025-0.1 g.

[0017] The principle of this technical solution is as follows:

[0018] In the selective oxidation of benzyl alcohol using air as the oxidant, the catalytic activity of a single-component cobalt oxide (CoOx) is low. This invention modifies the cobalt oxide using a significantly lower amount of Mn than Co, resulting in a two-component Mn-CoOx catalyst. During preparation, cobalt nitrate (a cobalt precursor) and manganese nitrate (a manganese precursor) are stirred and mixed with a solid dispersion medium, followed by high-temperature calcination. This allows the Co and Mn components in the resulting Mn-CoOx catalyst to fully combine and interact. Furthermore, at an Mn / Co molar ratio of 1:105 to 1:11, a significantly lower Mn content than Co can produce a significant modification effect, making the catalytic activity of the Mn-CoOx catalyst in the selective oxidation of benzyl alcohol significantly higher than that of the single-component CoOx catalyst. Mn-CoOx catalysts can activate oxygen dissolved in solvents to generate superoxide radicals. These superoxide radicals then react with benzyl alcohol molecules, efficiently activating them and thus achieving high catalytic activity. Simultaneously, the reaction of superoxide radicals with benzyl alcohol molecules also enables benzyl alcohol to be selectively converted into benzaldehyde.

[0019] The specific benefits of using the catalyst and benzyl alcohol catalytic oxidation method described in this scheme are as follows:

[0020] (1) Mn-CoOx catalyst can efficiently catalyze the selective oxidation of benzyl alcohol with air as oxidant, achieving 100% benzyl alcohol conversion and 100% benzaldehyde selectivity.

[0021] (2) The selective oxidation of benzyl alcohol catalyzed by the Mn-CoOx catalyst is very simple to operate. In the selective oxidation of benzyl alcohol, the Mn-CoOx catalyst disclosed in this invention can utilize oxygen dissolved in the solvent very efficiently, achieving both high catalytic activity and high benzaldehyde selectivity, thus eliminating the need for bubbling and pressurization techniques typically used to increase the amount of oxygen dissolved in the solvent. More specifically, the air, acting as the oxidant, exists at atmospheric pressure in the reactor space above the surface of the reaction mixture. It does not require a dedicated pipeline to introduce the air into the reactor or the reaction mixture, nor does it require pressurization to dissolve the air into the reaction mixture. The pressure inside the reactor remains at atmospheric pressure throughout the reaction.

[0022] (3) When catalyzing the selective oxidation of benzyl alcohol, the technical route disclosed in this invention does not require additional air, which can avoid the loss of solvent during the reaction, making it more environmentally friendly. It can also omit the solvent absorption device that must be equipped when introducing air or oxygen during the reaction, thus reducing equipment investment.

[0023] (4) Cobalt and manganese are both readily available non-precious metal elements with prices far lower than precious metals, which greatly reduces the cost of the process.

[0024] (5) This technical solution is the first to apply the solid-phase reaction method to prepare a catalyst, which can be used to catalyze the oxidation of benzyl alcohol to benzaldehyde. Compared with the coprecipitation method for preparing catalysts (e.g., Chinese patent CN105664926A), this solution does not have advantages in terms of the simplicity, repeatability, economy, and reliability of the preparation process. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; the materials and reagents used are all commercially available. More specifically, the chemical reagents mentioned in the present invention, such as cobalt nitrate, cobalt acetate, cobalt oxalate, manganese nitrate, manganese acetate, manganese oxalate, benzyl alcohol, toluene, acetonitrile, dichloromethane, F127, P123, F68, graphite powder, and sodium oxalate, were all purchased from commercial sources such as Aldrich and Shanghai Titan Technology Co., Ltd., and were used directly after receipt.

[0026] Example 1

[0027] The Mn-CoOx catalyst was prepared according to the following steps:

[0028] (1) Mix 10g of F127, cobalt nitrate, and manganese nitrate together, with a Mn / Co molar ratio of 1:11 and a F127 / (Co-Mn) molar ratio of 1:10 between the total amount of metals in the precursor and F127. Stir until homogeneous. That is, the ratio of the molar number of the solid dispersant to the sum of the molar numbers of cobalt in the cobalt precursor and manganese in the manganese precursor is 1:10.

[0029] (2) The mixture obtained above was calcined at 400℃ for 3h to obtain the Mn-CoOx catalyst. Air was introduced during the calcination process. At this temperature, the dispersant F127 was completely burned.

[0030] Mn-CoOx-catalyzed selective oxidation of benzyl alcohol:

[0031] 15 mL of toluene (as solvent), 0.12 mL of benzyl alcohol (reactant), and 0.05 mL of n-decane (internal standard) were added to the reactor, followed by 0.1 g of Mn-CoOx catalyst. The reactor was heated to 91 °C for 18 h, with the reaction mixture continuously stirred at 300 r / min. A room-temperature water condenser was connected to the reactor to cool the solvent under reflux.

[0032] The air remaining in the reaction apparatus, which consists of a condenser and a reactor, is the oxidant for the selective oxidation of benzyl alcohol. The pressure inside the reaction apparatus is maintained at atmospheric pressure during the reaction process.

[0033] A small rubber balloon, approximately 5 ml in volume, is attached to the upper outlet of the condenser. Its functions are: first, to act as a seal, preventing air circulation between the inside and outside of the reaction apparatus and ensuring no additional air is introduced during the reaction; second, to directly reflect the pressure state inside the reactor during the reaction—the balloon did not show significant inflation during the reaction, remaining relatively loose, indicating that the pressure inside the reactor is maintained at atmospheric pressure; third, to prevent solvent evaporation during the reaction, and to eliminate the need for a solvent absorption device that would otherwise be necessary when introducing air or oxygen during the reaction; and fourth, to act as a pressure safety device, preventing accidents caused by a rapid increase in reactor pressure due to unexpected malfunctions such as overheating that cannot be released.

[0034] After the reaction was completed, the heating of the reaction apparatus was stopped, and the reaction mixture was allowed to cool to room temperature. The catalyst in the reaction mixture was then separated and recovered by filtration. The reaction mixture after catalyst separation was analyzed by gas chromatography to obtain catalytic performance data such as benzyl alcohol conversion and benzaldehyde selectivity. Quantitative chromatographic analysis was performed using the internal standard method, with n-decane as the internal standard.

[0035] The Mn / Co molar ratio of cobalt and manganese precursors used in the catalyst preparation process of Examples 2-12 and Comparative Example 1 is different from that in Example 1. The types of cobalt and manganese precursors used in Examples 2, 3, and 5 are different from those in Example 1. The rest of the preparation process and parameters, and the catalytic reaction operation process are the same (see Example 1). The relevant data are shown in Table 1.

[0036] Comparative Examples 3-5 used F68, P123, and graphite powder as dispersants. The calcination temperature for catalyst preparation was increased to 450-500℃ to ensure complete combustion of the dispersant. The remaining operations were the same as those in the above examples.

[0037] Comparative Example 6 prepared a CoMn catalyst using a coprecipitation method with sodium oxalate as the precipitant. The Mn / Co molar ratio was 1:11. Cobalt nitrate and manganese nitrate solutions were mixed evenly, and then 1M sodium oxalate solution was slowly added dropwise. After precipitation at room temperature for 10 hours, the catalyst was filtered and washed, and then dried at 100°C for 10 hours. The remaining operations were the same as in Example 1 above (calcination and catalytic reaction of benzyl alcohol).

[0038] Comparative Examples 7-9 used nitrogen to purge the air from the reaction apparatus, so that only nitrogen remained in the reaction apparatus during the reaction process. The remaining operations were the same as in the above examples.

[0039] Table 1: Process parameter settings and test results for Examples 1-15 and Comparative Examples 1-5

[0040]

[0041] XRD analysis of the catalysts prepared in Examples 1-12 and Comparative Example 1 showed that only CoCo2O4 species were detected, and no manganese oxide species were observed to be generated. This is because the amount of manganese used in the technical solution was significantly lower than that of cobalt, and the manganese oxide species generated during the preparation process were highly dispersed in the CoCo2O4 species.

[0042] In the technical solution adopted in this invention, the oxidant is the air remaining in the reaction device, the reaction is carried out at atmospheric pressure, and only simple stirring of the reaction mixture is required to obtain benzaldehyde selectivity maintained at 100%. When there is no air in the reaction device, the benzyl alcohol conversion rate and benzaldehyde selectivity measured after the reaction are both 0 (Comparative Examples 7-9).

[0043] The catalytic activity of the Mn-CoOx catalyst is significantly higher than that of the single-component cobalt oxide prepared without the addition of Mn (Comparative Example 1).

[0044] When the Mn / Co molar ratio is 1:11, the conversion rate of benzyl alcohol by the Mn-CoOx catalyst reaches 100%.

[0045] The molar ratio of manganese to cobalt in the manganese precursor and cobalt precursor is 1:105-1:11, which can guarantee 100% selectivity for benzaldehyde (Examples 1-6).

[0046] The molar ratio of manganese to cobalt in the manganese and cobalt precursors is 1:33-1:11, which can further ensure a benzyl alcohol conversion rate of over 90% (Examples 1-3).

[0047] Maintaining the temperature of the benzyl alcohol catalytic oxidation reaction at around 91°C and the reaction time at 18 h can also significantly improve the benzyl alcohol conversion rate in the benzyl alcohol catalytic oxidation process (comparison between Example 7 and Example 1).

[0048] During the preparation of the catalyst, the calcination temperature was maintained at around 400°C, which can significantly improve the conversion rate of benzyl alcohol in the catalytic oxidation process (comparison between Example 8 and Example 1).

[0049] Furthermore, the choice of solvent in the catalytic oxidation process of benzyl alcohol significantly affects the conversion rate of benzyl alcohol and the selectivity of benzaldehyde, with toluene being the optimal choice (comparison between Examples 9-10 and Example 1).

[0050] The reaction time of the catalytic oxidation of benzyl alcohol significantly affects the conversion rate of benzyl alcohol and the selectivity of benzaldehyde. The highest conversion rate of benzyl alcohol can be achieved when the reaction time is 18 hours (comparison between Examples 11-12 and Example 1).

[0051] The calcination time during the preparation of Mn-CoOx catalyst significantly affects the benzyl alcohol conversion and benzaldehyde selectivity in the selective oxidation of benzyl alcohol. The highest benzyl alcohol conversion can be achieved when the calcination time is 3h (comparison of Examples 8, 13 and Example 1).

[0052] This technical solution is the first application of a solid-phase reaction method to prepare a manganese-modified cobalt oxide catalyst (Mn-CoOx catalyst), which can be used to catalyze the oxidation of benzyl alcohol to benzaldehyde. During the preparation of this catalyst, the inventors found that the choice of dispersant is crucial for improving the conversion rate of benzyl alcohol. Only by using F127 can the generated manganese oxide species be highly dispersed in the CoCo2O4 species and achieve a high benzyl alcohol conversion rate, even with trace amounts of Mn added. Other dispersants were less effective, affecting the efficiency of catalyzing the conversion of benzyl alcohol to benzaldehyde (Comparative Examples 3-5). The manganese-modified cobalt oxide catalyst prepared by the solid-phase reaction method, compared to the catalyst obtained by the co-precipitation method (Comparative Example 6), exhibits higher efficiency and a higher benzyl alcohol conversion rate when air is used as the oxidant. This demonstrates that only by employing a specific synthesis method (solid-phase synthesis and the use of a specific solid-phase dispersant) can a catalyst with ideal performance be obtained.

[0053] Furthermore, increasing the amount of Mn added reduces the conversion rate of benzyl alcohol in the catalyst obtained under the process conditions of this scheme. This indicates that the process conditions of this scheme are suitable for trace Mn doping (Comparative Example 2). If a large amount of Mn is required to prepare the catalyst, significant adjustments need to be made to the process conditions and raw material usage to generate novel catalysts.

[0054] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a manganese-modified cobalt oxide catalyst for the selective oxidation of benzyl alcohol, characterized in that: The steps are as follows, performed sequentially: S1: Mix cobalt precursor, manganese precursor and solid dispersion medium to obtain a mixture; and the molar ratio of manganese and cobalt elements in the manganese precursor and cobalt precursor is 1:33-1:11; the solid dispersion medium is any one of F127, P123, F68 and graphite powder; S2: Calcine the mixture to obtain a manganese-modified cobalt oxide catalyst Mn-CoOx; the calcination temperature is 300-400℃ and the time is 2-4h; and air is introduced during the calcination process; The manganese-modified cobalt oxide catalyst Mn-CoOx comprises cobalt oxide and manganese element highly dispersed in the cobalt oxide.

2. The preparation method according to claim 1, characterized in that: In S1, the cobalt precursor is any one of cobalt nitrate, cobalt acetate, and cobalt oxalate; the manganese precursor is any one of manganese nitrate, manganese acetate, and manganese oxalate.

3. A manganese-modified cobalt oxide catalyst Mn-CoOx prepared by the method for preparing a manganese-modified cobalt oxide catalyst for selective oxidation of benzyl alcohol according to claim 1 or 2.

4. A method for the selective oxidation of benzyl alcohol by the manganese-modified cobalt oxide catalyst Mn-CoOx according to claim 3, characterized in that: Benzyl alcohol and manganese-modified cobalt oxide catalyst Mn-CoOx are added to a solvent to obtain a reaction mixture. Air is used as the oxidant, and the reaction is carried out at 50-91°C and atmospheric pressure for 5-18 hours. Air exists in the reactor space above the liquid surface of the reaction mixture at atmospheric pressure. The reactor is a closed system, and no air is added during the reaction. The solvent is any one of toluene, acetonitrile, and dichloromethane.

5. The method for selective oxidation of benzyl alcohol by the manganese-modified cobalt oxide catalyst Mn-CoOx according to claim 4, characterized in that: The ratio of benzyl alcohol to manganese-modified cobalt oxide catalyst Mn-CoOx is 0.12-0.24 mL: 0.025-0.1 g.

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