Cerium-manganese bimetallic catalyst, preparation thereof and application of cerium-manganese bimetallic catalyst in catalyzing ozonized lignin to be converted into aromatic aldehyde

Abstract

The invention relates to the technical field of organic synthesis, in particular to a cerium-manganese bimetallic catalyst, preparation of the cerium-manganese bimetallic catalyst and application of the cerium-manganese bimetallic catalyst in catalyzing ozonized lignin to be converted into aromatic aldehyde. The cerium-manganese bimetallic catalyst provided by the invention has a large number of surface oxygen holes, and can convert herbal lignin into high-added-value aromatic aldehydes such as p-hydroxybenzaldehyde, vanillin and the like at high selectivity and high conversion rate under mild conditions; the catalytic system has good catalytic stability and substrate applicability. Compared with the prior art, under the action of the cerium-manganese bimetallic catalyst provided by the invention, the conversion rate of lignin and the selectivity of high-added-value aromatic aldehyde are remarkably improved; meanwhile, the catalyst is simple to prepare, wide in raw material source, stable and easy to store; when the catalyst is used for preparing high-added-value aromatic aldehyde through conversion of herbal lignin, the catalyst has high selectivity and high activity under mild conditions, and has good application value.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and particularly to a cerium-manganese bimetallic catalyst and its preparation, as well as its application in catalytic ozonation for converting lignin into aromatic aldehydes. Background Art

[0002] Nowadays, the massive consumption of non-renewable energy represented by petroleum and natural gas has caused the world to face an increasingly serious energy crisis, and people have never stopped exploring renewable energy. As a renewable resource with extremely rich reserves in nature, lignocellulosic biomass has great potential to replace fossil fuels for the production of fuels and chemicals. Only a very small part (20%) of industrial waste has been effectively utilized worldwide. Therefore, lignocellulosic biomass (such as grass, hardwood, and softwood) has high potential value in dealing with energy shortages and other aspects. Lignocellulosic biomass is composed of lignin, cellulose, and hemicellulose. Cellulose and hemicellulose are widely used in the paper-making and biorefining industries. However, most lignin is still mainly used as low-grade waste for combustion treatment, which undoubtedly causes a large amount of energy waste and other problems.

[0003] Lignin is a structurally complex C, H, O layered long-chain heterogeneous polymer, which is composed of three basic phenylpropane structural units, namely H unit (p-hydroxyphenyl unit), S unit (syringyl unit), and G unit (guaiacyl unit), connected to each other through various chemical bonds (such as β-O-4, β-β, α-O-4, etc.). There are also obvious differences in the specific structure and content of lignin in the structures of different lignocellulosic biomasses. Among them, herbaceous lignin is widely present in the cell walls of crop straws, fruit peels, bamboo, etc. Its structure contains a typical C=C double bond structure, and also contains connection bonds such as β-O-4, β-β, α-O-4. It should be noted that lignin is the only natural renewable source of aromatic rings in nature. From the perspective of atom economy, the rational utilization of lignin can increase the utilization value of biomass by 15-25%.

[0004] Currently, a variety of different strategies have been used for the valorization of lignin. For example, biomass fuels and various fuel additives are obtained through the hydrogenolysis of lignin, and aromatic small molecule compounds such as aromatic acids and aromatic aldehydes are obtained through the oxidation of lignin. However, the conventional hydrogenolysis and oxidative depolymerization of lignin generally require the use of a large amount of alkali, high temperature, and the catalytic action of noble metal catalysts. In addition, an additional hydrogen source or hydrogen peroxide, oxygen, and various peroxidases are required as oxygen sources. The harsh reaction conditions, expensive enzymes, noble metal catalysts, and the generation of a large amount of wastewater during the post-treatment process limit the large-scale development of lignin depolymerization.

[0005] Therefore, it is crucial to provide a technical solution that can solve the above problems. SUMMARY OF THE INVENTION

[0006] In order to solve the above problems, the object of the present invention is to provide a cerium-manganese bimetallic catalyst and its preparation, as well as its application in the catalytic ozonation of lignin to convert it into aromatic aldehydes. The cerium-manganese bimetallic catalyst provided by the present invention has high activity, simple and easily available synthetic raw materials, and low price; at the same time, the reaction conditions for the catalytic ozonation of herbaceous lignin are mild, the reaction selectivity is high, and good catalytic effects can be obtained for lignins extracted from a variety of herbaceous plants.

[0007] As a strong oxidant, ozone can efficiently depolymerize complex organic substances under mild conditions, thus avoiding a large amount of wastewater and toxic by-products generated during the post-treatment process. In particular, ozone can selectively oxidize the C═C double bond in organic substances into aldehyde groups without destroying other chemical bonds. Moreover, ozone can be converted into superoxide radicals under the action of transition metal oxide catalysts, and the superoxide radicals can efficiently depolymerize the β-O-4 units in the lignin structure, thereby generating aromatic aldehydes. The present invention aims at the structure containing C═C double bonds in herbaceous lignin, so that catalytic ozonation can convert the C═C double bond into aromatic aldehydes under mild conditions while catalytically ozonating a small amount of β-O-4 bonds contained, converting lignin into high-value-added aromatic aldehydes and improving the comprehensive utilization rate of lignin.

[0008] The object of the present invention can be achieved by the following technical solutions:

[0009] The first object of the present invention is to provide a preparation method of a cerium-manganese bimetallic catalyst, comprising the following steps:

[0010] (S1) Dissolve cerium salt, manganese salt and complexing agent and mix them evenly, adjust the pH to neutral, stir until it becomes a gel state, and then carry out drying treatment to obtain a dry gel;

[0011] (S2) Place the dry gel prepared in step (S1) in an air atmosphere for calcination treatment to obtain a cerium-manganese bimetallic catalyst.

[0012] In one embodiment of the present invention, in step (S1), the cerium salt is selected from one or more of cerium nitrate, cerium sulfate or cerium chloride;

[0013] The manganese salt is selected from one or more of manganese nitrate, manganese sulfate or manganese chloride;

[0014] The complexing agent is selected from one or more of citric acid, maleic acid or ascorbic acid.

[0015] In one embodiment of the present invention, in step (S1), the molar ratio of cerium salt to manganese salt is 1-10:1-10;

[0016] The molar ratio of the total amount of the complexing agent, cerium salt and manganese salt is 1: 0.5-5;

[0017] During the stirring process, the temperature is 40-90 °C and the time is 0.5-5 h;

[0018] During the drying process, the temperature is 100-130 °C.

[0019] In one embodiment of the present invention, ammonia water with a concentration of 20-30 wt% is used to adjust the pH to neutral.

[0020] In one embodiment of the present invention, in step (S2), during the calcination process, the heating rate is 2-5 °C / min, the temperature is 300-600 °C, and the time is 1-5 h.

[0021] The second object of the present invention is to provide a cerium-manganese bimetallic catalyst prepared by the above method.

[0022] The third object of the present invention is to provide an application of the cerium-manganese bimetallic catalyst in the catalytic ozonation of lignin to convert it into aromatic aldehydes.

[0023] The fourth object of the present invention is to provide a method for catalytic ozonation of lignin to convert it into aromatic aldehydes by using a cerium-manganese bimetallic catalyst, comprising the following steps:

[0024] Dissolve the above-mentioned cerium-manganese bimetallic catalyst and lignin in a solvent, then place it in an ozone atmosphere, mix well and carry out the reaction, and after the reaction, perform post-treatment to obtain aromatic aldehydes.

[0025] In one embodiment of the present invention, the solvent is selected from one or more of methanol, ethanol, ethyl acetate, dichloromethane or acetonitrile;

[0026] The lignin structure contains syringyl units, guaiacyl units, p-hydroxyphenol units and lignin-carbohydrate complex units composed of ferulic acid and p-coumaric acid;

[0027] The lignin is selected from one or more of moso bamboo lignin, corn cob lignin, rice straw lignin, corn straw lignin or wheat straw lignin.

[0028] In one embodiment of the present invention, the mass ratio of the cerium-manganese bimetallic catalyst to lignin is 1: 50-200;

[0029] During the reaction process, the pressure is normal pressure, the temperature is -20-10 °C, and the time is 1-10 min.

[0030] In one embodiment of the present invention, after filtering out the cerium-manganese bimetallic catalyst in the reaction solution, a reducing agent is added to the solution to terminate the reaction;

[0031] Among them, the reducing agent is selected from one or more of triphenylphosphine, sodium metabisulfite, sodium sulfite, sodium thiosulfate, sodium sulfide or dimethyl sulfide.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The Ce-Mn bimetallic oxide catalyst of the present invention improves the activity of the catalyst through the interaction between Ce and Mn in the crystal structure of the catalyst, thereby effectively ensuring the reaction selectivity and enhancing the reaction efficiency accordingly.

[0034] (2) The reaction conditions of this reaction process are very mild, the reaction is rapid and highly selective, and it has good application prospects.

[0035] (3) The catalytic ozonation of herbaceous lignin and ozone using this catalyst is applicable to lignin in a variety of different herbaceous plants, and the substrate has a wide range of practical applications. Description of the Drawings

[0036] Figure 1 XRD comparison diagrams of the metal catalysts prepared in Example 1, Example 3, Example 8 and Comparative Example 1;

[0037] Figure 2 MnO in Example 3 x Change diagrams of surface oxygen vacancies Ov and chemisorbed oxygen Oads of O1s caused by the incorporation of Ce in the catalyst;

[0038] Figure 3 Schematic diagram of the active oxygen species generated by ozone on the surface of cerium-manganese bimetallic oxide detected by EPR in Example 3;

[0039] Figure 4 Two-dimensional HSQC NMR diagrams of corn straw lignin before and after catalytic ozonation treatment in Example 7. Detailed Embodiments

[0040] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0041] In the following embodiments, unless otherwise specified, the reagents used are commercially available reagents, and the detection means and methods used are conventional detection means and methods in the art.

[0042] Example 1

[0043] This example relates to a preparation method of a cerium-manganese bimetallic catalyst, which specifically includes the following steps:

[0044] (S1) Dissolve MnSO4 (0.06 mol), Ce2(SO4)3 (0.01 mol) and maleic acid (0.07 mol) in 100 mL of deionized water to form a homogeneous solution. Slowly add 20 wt% ammonia water until the pH of the solution reaches 7, and then stir at 60 °C for 1 h until a stable gel is formed. Then dry the gel at 130 °C to obtain a dry, porous beige gel.

[0045] (S2) Place the dry, porous purple gel prepared in step (S1) in a muffle furnace for calcination. Under an air atmosphere, heat from room temperature to 500 °C at a heating rate of 2 °C / min and hold for 3 h to obtain a cerium-manganese bimetallic catalyst: CeMn6O x (XRD pattern as Figure 1 shown).

[0046] It can be found through Figure 1 that the intensities of the diffraction peaks at 2θ = 17.9°, 44.5°, 50.8° and 64.6° are respectively attributed to the diffraction peaks of the (101), (220), (105) and (400) crystal planes of Mn3O4.

[0047] Example 2

[0048] This example provides a method for the catalytic ozonation of lignin to aromatic aldehydes using a cerium-manganese bimetallic catalyst, which includes the following steps:

[0049] (1) Add methanol (99 g), CeMn6O x (prepared in Example 3, 0.02 g), a magnetic stir bar and corncob lignin (1 g) into a glass jacketed reactor (250 mL) and externally connect a cooling circulating water to cool down to 0 °C.

[0050] (2) Turn on the power of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator (SDK0-10) remains unchanged, thereby ensuring the ozone concentration. The used ozone generator uses dry air as the raw material and produces approximately 160 mg / min of ozone through electrode discharge.

[0051] (3) Turn on the stirrer and introduce ozone, and control the reaction temperature to carry out the reaction at 0 °C for 8 min. After the reaction is completed, add 20 wt% aqueous dimethyl sulfide solution to quench, and use a moist KI test paper to detect whether the quenching is completed. Then, qualitative and quantitative analyses are carried out by HPLC. HPLC analysis shows that the yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate and syringaldehyde after the catalytic ozonation of corncob lignin by CeMn6Ox are 10.31 wt%, 2.96 wt%, 1.27 wt%, 1.33 wt% and 2.74 wt% respectively.

[0052] Example 3

[0053] This example relates to a preparation method of a cerium-manganese bimetallic catalyst, specifically including the following steps:

[0054] (S1) Dissolve Mn(CH3COO)2·4H2O (0.04 mol), Ce(NO3)·6H2O (0.01 mol) and ascorbic acid (0.05 mol) in 100 mL of deionized water to form a homogeneous solution, slowly add 28 wt% ammonia water until the pH of the solution is 7, and then stir at 90 °C for 1 h until a stable gel is formed; then dry the gel at 120 °C to obtain a dry porous beige gel;

[0055] (S2) Place the dry porous purple gel prepared in step (S1) in a muffle furnace for calcination treatment, and heat from room temperature to 400 °C at a heating rate of 3 °C / min in an air atmosphere and hold for 5 h to obtain a cerium-manganese bimetallic catalyst: CeMn4O x (The XRD pattern is as shown in Figure 1 ).

[0056] It can be found through Figure 1 that the intensities of the diffraction peaks at 2θ = 17.9°, 44.5°, 50.8° and 64.6° respectively belong to the diffraction peaks of the (101), (220), (105) and (400) crystal planes of Mn3O4.

[0057] It can be found through Figure 2 that the main peak obtained after deconvolution of the O 1s orbital on the surface of MnO x is located at around 529.5 eV, which is caused by the lattice oxygen on the surface of MnOx. In addition, two small peaks located at 531.5 and 533.5 eV are also observed, which are caused by the oxygen vacancies and chemically adsorbed oxygen on the surface of MnO x respectively. When Ce is introduced into MnO x , the intensity of the peak belonging to oxygen vacancies on the surface of CeMn4O x is stronger than that of MnO x . At the same time, the peak belonging to lattice oxygen on the surface of CeMn4O x shifts to a lower binding energy, which may be due to CeO2 on the surface of CeMn4O x .

[0058] Figure 3 Figure x is the EPR quantitative diagram of the active oxygen species generated on the surface of CeMn4O - . An obvious sextet signal belonging to ·O2 xAfter doping with Ce, it can indeed convert ozone into ·O2 - .

[0059] Example 4

[0060] This example provides a method for catalytic ozonation of lignin with a cerium-manganese bimetallic catalyst to convert it into aromatic aldehydes, including the following steps:

[0061] (1) Add methanol (198 g), CeMn4O x (prepared in Example 3, 0.2 g), a magnetic stir bar, and moso bamboo lignin (2 g) into a glass jacketed reactor (250 mL), and externally connect a cooling circulating water to cool it down to 10 °C;

[0062] (2) Turn on the power supply of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator (SDK0-10) remains unchanged, thereby ensuring the ozone concentration; the used ozone generator uses dry air as the raw material and produces approximately 160 mg / min of ozone through electrode discharge.

[0063] (3) Turn on the stirring and introduce ozone, and control the reaction temperature to react at 10 °C for 7 min. After the reaction is completed, add 10 wt% aqueous dimethyl sulfide solution to quench, and use a moist KI test paper to detect whether the quenching is completed; then perform qualitative and quantitative analysis by HPLC. HPLC analysis shows that after the catalytic ozonation of corncob lignin with CeMn4O x The yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde are 9.19 wt%, 3.27 wt%, 2.29 wt%, 2.37 wt%, and 2.45 wt%, respectively.

[0064] Example 5

[0065] This example provides a method for catalytic ozonation of lignin with a cerium-manganese bimetallic catalyst to convert it into aromatic aldehydes, including the following steps:

[0066] (1) Add ethyl acetate (99 g), CeMn4O x (prepared in Example 3, 0.1 g), a magnetic stir bar, and wheat straw lignin (1 g) into a glass jacketed reactor (250 mL), and externally connect a cooling circulating water to cool it down to 0 °C;

[0067] (2) Turn on the power supply of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator (SDK0-10) remains unchanged, thereby ensuring the ozone concentration; the used ozone generator uses dry air as the raw material and produces approximately 160 mg / min of ozone through electrode discharge.

[0068] (3) Start stirring and introduce ozone. Control the reaction temperature at 0 °C and carry out the reaction for 5 min. After the reaction is completed, add 10 wt% aqueous dimethyl sulfide solution to quench, and use a moist KI test paper to detect whether the quenching is completed; then perform qualitative and quantitative analysis by HPLC. HPLC analysis shows that after the catalytic ozonation of wheat straw lignin with CeMn4O x the yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde are 4.03 wt%, 0.96 wt%, 0.40 wt%, 0.38 wt%, and 0.60 wt%, respectively.

[0069] Example 6

[0070] This example provides a method for the catalytic ozonation of lignin to aromatic aldehydes using a cerium-manganese bimetallic catalyst, which includes the following steps:

[0071] (1) Add dichloromethane (99 g), CeMn4O x (prepared in Example 3, 0.01 g), a magnetic stir bar, and wheat straw lignin (1 g) into a glass jacketed reactor (250 mL), and externally connect a cooling circulating water to cool down to -10 °C;

[0072] (2) Turn on the power supply of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator remains unchanged, thereby ensuring the ozone concentration; the used ozone generator uses dry air as the raw material and produces approximately 160 mg / min of ozone through electrode discharge.

[0073] (3) Start stirring and introduce ozone. Control the reaction temperature at -10 °C and carry out the reaction for 4 min. After the reaction is completed, add 15 wt% aqueous sodium bisulfite solution to quench, and use a moist KI test paper to detect whether the quenching is completed; then perform qualitative and quantitative analysis by HPLC. HPLC analysis shows that after the catalytic ozonation of rice straw lignin with CeMn4O x the yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde are 3.63 wt%, 1.06 wt%, 0.51 wt%, 0.52 wt%, and 0.63 wt%, respectively.

[0074] Example 7

[0075] This example provides a method for the catalytic ozonation of lignin to aromatic aldehydes using a cerium-manganese bimetallic catalyst, which includes the following steps:

[0076] (1) Add acetonitrile (99 g), CeMn4O x(Prepared in Example 3, 0.01 g), magnetic stir bar and corn stover lignin (1 g) were added to a glass jacketed reactor (250 mL) and the external cooling circulating water was lowered to 5 °C;

[0077] (2) Turn on the power of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator (SDK0-10) remains unchanged so as to ensure the ozone concentration; the used ozone generator uses dry air as raw material and produces about 160 mg / min ozone through electrode discharge.

[0078] (3) Turn on the stirring and introduce ozone, control the reaction temperature at 5 °C and react for 5 min. After the reaction, 10 wt% triphenylphosphine aqueous solution was added to quench, and a moist KI test paper was used to detect whether the quenching was completed; then qualitative and quantitative analysis was carried out by HPLC. HPLC analysis showed that the yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate and syringaldehyde were 3.74 wt%, 0.96 wt%, 0.51 wt%, 0.49 wt% and 0.65 wt% respectively after the catalytic ozonation of corn stover lignin. x The yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate and syringaldehyde were 3.74 wt%, 0.96 wt%, 0.51 wt%, 0.49 wt% and 0.65 wt% respectively after the catalytic ozonation of corn stover lignin.

[0079] Figure 4 Figures 2 and 3 are two-dimensional HSQC NMR spectra of corn stover lignin before and after catalytic ozonation in Example 7. It can be found that after the ozonation of corn stover lignin, the signals belonging to pCA, FA, FA2 and FA6 in the herbaceous lignin structure at δ H / C = 7.53 / 144.83, 7.30 / 145.27, 7.33 / 111.59, 7.12 / 123.62 decreased significantly or even disappeared. In addition, new NMR signals appeared at δ H / C = 7.77 / 132.08 and 7.38 / 111.93, which belong to p-hydroxybenzaldehyde and vanillin respectively. Figure 4 It can be found that after the ozonation of corn stover lignin, the signals belonging to pCA, FA, FA2 and FA6 in the herbaceous lignin structure at δ H / C = 7.53 / 144.83, 7.30 / 145.27, 7.33 / 111.59, 7.12 / 123.62 decreased significantly or even disappeared. 1 H / 13 C = 7.53 / 144.83, 7.30 / 145.27, 7.33 / 111.59, 7.12 / 123.62 belonging to pCA, FA, FA2 and FA6 in the herbaceous lignin structure α 、FA α 、FA2 and FA6 in the herbaceous lignin structure decreased significantly or even disappeared. In addition, new NMR signals appeared at δ H / C = 7.77 / 132.08 and 7.38 / 111.93, which belong to p-hydroxybenzaldehyde and vanillin respectively. 1 H / 13 C = 7.77 / 132.08, 7.38 / 111.93 belong to p-hydroxybenzaldehyde and vanillin respectively.

[0080] Example 8

[0081] This example relates to a preparation method of a cerium-manganese bimetallic catalyst, which specifically includes the following steps:

[0082] (S1) Dissolve Mn(CH3COO)2·4H2O (0.02 mol), Ce(CH3COO)3·4H2O (0.01 mol) and citric acid (0.03 mol) in 100 mL of deionized water to form a homogeneous solution. Slowly add 24 wt% ammonia water until the pH reaches 7, and then stir at 80 °C for 1 h until a stable gel is formed. Then dry the gel at 100 °C to obtain a dry and porous beige gel;

[0083] (S2) Place the dry and porous purple gel prepared in step (S1) in a muffle furnace for calcination. Under an air atmosphere, heat from room temperature to 500 °C at a heating rate of 4 °C / min and hold for 4 h to obtain a cerium-manganese bimetallic catalyst: CeMn2O x (The XRD pattern is as shown in Figure 1 ).

[0084] It can be found through Figure 1 that the intensities of the diffraction peaks at 2θ = 17.9°, 44.5°, 50.8° and 64.6° respectively belong to the diffraction peaks of the (101), (220), (105) and (400) crystal planes of Mn3O4. Compared with several other catalysts, as the Ce content continuously increases, the intensity of the Mn diffraction peak gradually weakens and even almost completely disappears. The (112) crystal plane of Mn3O4 at 2θ = 29.2° is gradually replaced by the (111) crystal plane of CeO2, and the intensities of the diffraction peaks belonging to the (220) and (311) planes of CeO2 at 2θ = 47.5° and 56.5° also gradually increase with the increase of the Ce content.

[0085] Example 9

[0086] This example provides a method for catalytic ozonation of lignin to aromatic aldehydes using a cerium-manganese bimetallic catalyst, which includes the following steps:

[0087] (1) Add methanol (198 g), CeMn2O x (prepared in Example 8, 0.2 g), a magnetic stir bar and bamboo lignin (2 g) into a glass jacketed reactor (250 mL) and externally connect a cooling circulating water to cool down to 0 °C;

[0088] (2) Turn on the power supply of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator (SDK0-10) remains unchanged to ensure the ozone concentration; the used ozone generator uses dry air as the raw material and produces about 160 mg / min of ozone through electrode discharge.

[0089] (3) Start stirring and introduce ozone. Control the reaction temperature at 0 °C and carry out the reaction for 6 min. After the reaction is completed, add 20 wt% aqueous sodium metabisulfite solution to quench, and use a moist KI test paper to detect whether the quenching is complete; then perform qualitative and quantitative analysis by HPLC. The HPLC analysis shows that the yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde are 4.07 wt%, 0.92 wt%, 0.43 wt%, 0.47 wt%, and 0.67 wt%, respectively, after the catalytic ozonation of moso bamboo lignin with MnO x The yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde are 4.07 wt%, 0.92 wt%, 0.43 wt%, 0.47 wt%, and 0.67 wt%, respectively, after the catalytic ozonation of moso bamboo lignin with MnO

[0090] Comparative Example 1

[0091] This comparative example relates to a preparation method of a single-metal (manganese) catalyst, which specifically includes the following steps:

[0092] (S1) Dissolve Mn(NO3)2·4H2O (0.01 mol) and citric acid (0.01 mol) in 100 mL of deionized water to form a homogeneous solution. Slowly add 20 wt% ammonia water until the pH of the solution is 7, and then stir at 40 °C for 1 h until a stable gel is formed; then dry the gel at 130 °C to obtain a dry, porous white gel;

[0093] (S2) Place the dry, porous purple gel prepared in step (S1) in a muffle furnace for calcination. Heat it from room temperature to 600 °C at a heating rate of 5 °C / min in an air atmosphere and hold for 2 h to obtain a single-metal (manganese) catalyst: MnO x (The XRD pattern is as shown in Figure 1 )

[0094] It can be found through Figure 1 that the intensities of the diffraction peaks at 2θ = 17.9°, 44.5°, 50.8°, and 64.6° respectively belong to the diffraction peaks of the (101), (220), (105), and (400) crystal planes of Mn3O4.

[0095] Comparative Example 2

[0096] This comparative example provides a method for the catalytic ozonation of lignin to aromatic aldehydes using a single-metal (manganese) catalyst, which includes the following steps:

[0097] (1) Add methanol (198 g), MnO x (prepared in Comparative Example 1, 0.1 g), a magnetic stir bar, and moso bamboo lignin (2 g) to a glass jacketed reactor (250 mL) and externally connect a cooling circulating water to cool down to -20 °C;

[0098] (2) Turn on the power supply of the ozone generator and connect the cooling water to ensure that the electrode efficiency of the ozone generator (SDK0-10) remains unchanged, thereby ensuring the ozone concentration; the ozone generator used takes dry air as the raw material and produces approximately 160 mg / min of ozone through electrode discharge.

[0099] (3) Turn on the agitation and introduce ozone, and control the reaction temperature to carry out the reaction for 8 min under the condition of -20°C. After the reaction is completed, add a 5 wt% aqueous solution of triphenylphosphine to quench, and use a moist KI test paper to detect whether the quenching is completed; then carry out qualitative and quantitative analysis by HPLC. The HPLC analysis shows that the yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde after the catalytic ozonation of moso bamboo lignin are 3.96 wt%, 0.83 wt%, 0.40 wt%, 0.36 wt%, and 0.59 wt%, respectively. x The yields of p-hydroxybenzaldehyde, vanillin, methyl p-hydroxybenzoate, methyl vanillate, and syringaldehyde are 3.96 wt%, 0.83 wt%, 0.40 wt%, 0.36 wt%, and 0.59 wt%, respectively.

[0100] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the interpretation of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a cerium-manganese bimetallic catalyst, characterized in that, It includes the following steps: (S1) Dissolve cerium salt, manganese salt and complexing agent and mix them evenly, adjust the pH to neutral, stir until it becomes a gel state and then carry out drying treatment to obtain a dry gel; (S2) Place the dry gel prepared in step (S1) in an air atmosphere for calcination treatment to obtain a cerium-manganese bimetallic catalyst.

2. The preparation method of a cerium-manganese bimetallic catalyst according to claim 1, wherein In step (S1), the cerium salt is selected from one or more of cerium nitrate, cerium sulfate or cerium chloride; The manganese salt is selected from one or more of manganese nitrate, manganese sulfate or manganese chloride; The complexing agent is selected from one or more of citric acid, maleic acid or ascorbic acid.

3. The preparation method of a cerium-manganese bimetallic catalyst according to claim 1, characterized in that, In step (S1), the molar ratio of cerium salt to manganese salt is 1-10:1-10; The molar ratio of the total amount of the complexing agent, cerium salt and manganese salt is 1:0.5-5; During the stirring process, the temperature is 40-90 °C and the time is 0.5-5 h; During the drying treatment process, the temperature is 100-130 °C.

4. The preparation method of a cerium-manganese bimetallic catalyst according to claim 1, characterized in that, In step (S2), during the calcination process, the heating rate is 2-5 °C / min, the temperature is 300-600 °C, and the time is 1-5 h.

5. A cerium-manganese bimetallic catalyst, characterized in that, Prepared by the method according to any one of claims 1-4.

6. Use of the cerium-manganese bimetallic catalyst as claimed in claim 5 in the catalytic ozonation of lignin to convert it into aromatic aldehyde.

7. A method for catalytic ozonation of lignin to aromatic aldehydes using a cerium-manganese bimetallic catalyst, characterized in that, It includes the following steps: Dissolve the cerium-manganese bimetallic catalyst and lignin as claimed in claim 5 in a solvent, then place it in an ozone atmosphere, mix evenly and carry out the reaction, and after the reaction, carry out post-treatment to obtain aromatic aldehyde.

8. A method for catalytic ozonation of lignin to convert it into aromatic aldehydes using a cerium-manganese bimetallic catalyst according to claim 7, characterized in that, The solvent is selected from one or more of methanol, ethanol, ethyl acetate, dichloromethane or acetonitrile; The lignin is selected from one or more of moso bamboo lignin, corncob lignin, rice straw lignin, corn straw lignin or wheat straw lignin.

9. A method for catalytic ozonation of lignin into aromatic aldehydes using a cerium-manganese bimetallic catalyst according to claim 7, characterized in that, The mass ratio of the cerium-manganese bimetallic catalyst to lignin is 1:50-200; During the reaction process, the pressure is normal pressure, the temperature is -20-10 °C, and the time is 1-10 min.

10. A method for catalytic ozonation of lignin to convert it into aromatic aldehydes using a cerium-manganese bimetallic catalyst according to claim 7, characterized in that, Filter out the cerium-manganese bimetallic catalyst in the reaction solution and then add a reducing agent to the solution to terminate the reaction; Among them, the reducing agent is selected from one or more of triphenylphosphine, sodium metabisulfite, sodium sulfite, sodium thiosulfate, sodium sulfide or dimethyl sulfide.

Images