Preparation method and application of catalyst for producing aromatic aldehyde acid through alkali-free oxidation of agricultural lignin

Abstract

The invention discloses a preparation method and application of a catalyst for producing aromatic aldehyde acid through alkali-free oxidation of agricultural lignin, and belongs to the technical field of thermal catalytic conversion of lignin. The catalyst for producing aromatic aldehyde acid through alkali-free oxidation of agricultural lignin is a LaNiO3 / CeO2 catalyst, and CeO2 is used as a carrier of the catalyst. The LaNiO3 / CeO2 catalyst provided by the invention has good synergistic catalysis, high oxygen mobility and excellent oxidation-reduction performance, and can efficiently break beta-O-4 bonds of lignin, so that the LaNiO3 / CeO2 catalyst has good catalytic performance and is suitable for being used as a catalyst for preparing high-value aromatic aldehyde acid by alkali-free oxidation of agricultural lignin.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lignin thermal catalytic conversion, and more particularly relates to a preparation method of a catalyst for producing aromatic aldehyde acid from agricultural lignin by alkali-free oxidation and application thereof. BACKGROUND

[0002] At present, the process of preparing ethanol from cellulose and furfural from hemicellulose is mature, but the actual development and utilization of lignin with abundant reserves in nature is facing major challenges due to its highly cross-linked chemical properties. In order to break through the technical bottleneck of lignin depolymerization, researchers focus on the selective cleavage of the key chemical bond β-O-4 bond, and researchers have developed various cleavage pathways of the β-O-4 bond of lignin, such as liquefaction, pyrolysis, etc. Among them, the oxidation method in liquefaction can cleave the C α -C β / C β -O bond in the β-O-4 bond and retain the aromatic ring structure to produce aromatic aldehydes, aromatic acids and other aromatic compounds, and these aromatic compounds have important applications in the chemical, pharmaceutical and food industries.

[0003] Lignin oxidation reactions often involve the use of catalysts, and the developed catalysts mainly include metal oxides, noble metals (supported), transition metals (salts), organic complexes, rare earth perovskite oxides, etc. Among them, ABO3 type perovskites are favored by researchers in the field of catalysis due to their cost advantage, flexible lattice regulation, outstanding lattice oxygen migration ability and other advantages. However, the calcination at high temperature of perovskite materials leads to a low specific surface area, which also results in poor accessibility of active sites to lignin macromolecules. Moreover, the current lignin catalytic oxidation is mainly based on alkaline systems, which usually leads to the production of aromatic acids in the form of salts. In this case, additional acidification and purification steps are needed before industrial application, and a large amount of inorganic waste is generated, which brings cumbersome steps to subsequent product separation. In contrast, alcohol-water cosolvents are favored due to their low toxicity, economy and good solubility for lignin. Based on this, developing an alcohol-water cosolvent system to replace the alkaline system for the catalytic oxidation of lignin not only helps its depolymerization, but also has relatively less impact on the environment.

[0004] Therefore, it is necessary to provide a new high-activity catalyst for lignin catalytic oxidation and an oxidation reaction system. SUMMARY

[0005] The application aims to provide a preparation method of a catalyst for producing aromatic aldehyde acid by alkaline-free oxidation of agricultural lignin and application thereof, so as to solve the problems in the prior art.

[0006] To achieve the above object, the application provides the following solutions.

[0007] One of the technical solutions of the application is to provide a preparation method of a catalyst for producing aromatic aldehyde acid by alkaline-free oxidation of agricultural lignin, comprising the following steps.

[0008] The lanthanum source and the nickel source are dissolved in water to form solution A; citric acid is dissolved in water to form solution B; the solution A, the solution B, CeO2 and ethylene glycol are mixed and reacted to obtain a gel; the gel is dried, ground and calcined to obtain the catalyst for producing aromatic aldehyde acid by alkaline-free oxidation of agricultural lignin.

[0009] The ethylene glycol is selected because it is miscible with water to form a uniform solution, which is helpful for the dissolution of metal salts and reagents such as citric acid, thereby promoting the formation of the gel. In addition, the ethylene glycol can form a complex with metal ions, which is helpful for controlling the distribution of metal ions and preventing uneven precipitation or agglomeration of the metal ions during drying or calcination. In addition to ethylene glycol, glycerol can also be used as a solvent and complexing agent, but its molecular weight is larger, which will affect the shrinkage rate of the gel and the pore structure of the final product.

[0010] Preferably, the lanthanum source comprises La(NO3)3 and / or lanthanum acetate; and the nickel source comprises Ni(NO3)2 and / or nickel acetate.

[0011] Preferably, in the solution A, the concentrations of La 3+ and Ni 2+ are independently 0.06-0.08 mol / L; in the solution B, the concentration of citric acid is 0.144-0.192 mol / L; and the ratio of the total molar amount of La 3+ and Ni 2+ to the molar amount of citric acid is 1:1.2.

[0012] Preferably, the molar ratio of La 3+ , Ni 2+ and ethylene glycol is 1:1:0.5.

[0013] Preferably, the temperature of the reaction is 80-90℃; the temperature of the drying is 100-105℃, and the time is 11-13h; the time of the grinding is 8-10min; the calcination includes two stages; the first stage is pre-burning, the temperature of the pre-burning is 400-450℃, the heating rate is 3℃ / min, and the holding time is 2-3h; the temperature of the second stage is 700-750℃, the heating rate is 3℃ / min, and the holding time is 3-4h.

[0014] The second technical scheme of the present application provides a LaNiO3 / CeO2 catalyst prepared by the preparation method, wherein the loading amount of LaNiO3 is 5-40wt%.

[0015] The third technical scheme of the present application provides an application of the LaNiO3 / CeO2 catalyst in the production of aromatic aldehyde acid by the alkaline-free oxidation of agricultural lignin.

[0016] The fourth technical scheme of the present application provides a method for producing aromatic aldehyde acid by the alkaline-free oxidation of agricultural lignin, comprising the following steps:

[0017] Mixing the agricultural lignin, the LaNiO3 / CeO2 catalyst and the co-solvent, and then reacting under an oxygen atmosphere to obtain the aromatic aldehyde acid.

[0018] Preferably, the co-solvent is composed of isopropyl alcohol and water, and the volume ratio of the isopropyl alcohol to water is 1:0-1; the amount ratio of the agricultural lignin, the LaNiO3 / CeO2 catalyst and the co-solvent is 0.5-1g:0.1-0.4g:20-30mL.

[0019] Preferably, the pressure of the oxygen is 0.4-1.0MPa, the reaction time is 1-2h, and the reaction temperature is 120-200℃.

[0020] The LaNiO3 / CeO2 catalyst has CeO2 as a carrier, and CeO2 is a rare earth oxide with excellent oxygen storage performance. 4+ can reversibly convert into Ce 3+ , thereby generating oxygen vacancies, and the oxygen vacancies are beneficial to the adsorption and activation of molecular oxygen and promote the migration of oxygen species. Therefore, the CeO2-based catalyst can exhibit excellent catalytic performance in the production of aromatic aldehyde acid by the alkaline-free oxidation of agricultural lignin. In addition, the specific surface area of CeO2 is large, and the perovskite is loaded on CeO2, which can increase the contact area with lignin and thereby enhance the catalytic activity.

[0021] The LaNiO3 / CeO2 catalyst prepared by the method has the characteristics of synergistic catalysis, excellent oxygen species conduction and high activity, etc. When catalyzing the oxidation of agricultural lignin, the LaNiO3 / CeO2 catalyst makes full use of the surface acid-base site active center, the acid-base site is beneficial to the rupture of the C-C / C-O bond of lignin, and the oxygen vacancies on the surface of the LaNiO3 / CeO2 catalyst are used to adsorb and activate molecular oxygen, which is beneficial to the adsorption and activation of oxygen, thereby promoting the production of aromatic aldehyde acid, and therefore the LaNiO3 / CeO2 catalyst can efficiently catalyze the oxidation of agricultural lignin to generate high-value aromatic aldehyde acid.

[0022] The present application discloses the following technical effects:

[0023] (1) The catalyst preparation method has good chemical uniformity, high purity, simple process and easy implementation.

[0024] (2) The LaNiO3 / CeO2 catalyst has good synergistic catalysis, high oxygen migration rate and excellent oxidation-reduction performance, can efficiently break the beta-O-4 bond of lignin, and therefore has good catalytic performance and is suitable for being used as a catalyst for alkali-free oxidation of agricultural lignin.

[0025] (3) The present application further provides a method for producing aromatic aldehyde acid by alkali-free oxidation of agricultural lignin, and the reaction system is green, the reaction conditions are mild, controllability is good, and the catalytic effect is good. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The crystal structure and chemical structure spectrum of the LaNiO3 / CeO2, LaNiO3 and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2 are shown in the figures, wherein a is an XRD spectrum, b is a Raman spectrum, and c is an FTIR spectrum;

[0027] Figure 2 The N2 adsorption-desorption isotherm (a) and pore size distribution curve (b) of the LaNiO3 / CeO2, LaNiO3 and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2 are shown in the figures;

[0028] Figure 3 The XPS spectra of La 3d (a), Ni 2p (b), Ce 3d (c) and O1s (d) and the EPR spectrum (e) of the LaNiO3 / CeO2, LaNiO3 and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2 are shown in the figures;

[0029] Figure 4H2-TPR (a), CO2-TPD (b) and NH3-TPD (c) profiles of the different loading LaNiO3 / CeO2, LaNiO3, CeO2 catalysts prepared for Examples 1-4 and Comparative Examples 1-2;

[0030] Figure 5 Oxidation activity plots of the different loading LaNiO3 / CeO2, LaNiO3, CeO2 catalysts prepared for Examples 1-4 and Comparative Examples 1-2, without base catalysis CAL, where a is CAL conversion, b is liquid oil yield, c is solid product residue, d is aromatic aldehyde acid yield;

[0031] Figure 6 2D HSQC NMR spectra of CAL and liquid product obtained after base catalytic oxidation of CAL with / without the different loading LaNiO3 / CeO2, LaNiO3, CeO2 catalysts prepared for Examples 1-4 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0032] The following detailed description is provided to understand the various example embodiments of the present application, which should not be considered limiting, but rather as a description of certain aspects, features and embodiments of the present application.

[0033] It should be understood that the terms used in the specification are for the purpose of describing particular embodiments only and are not intended to be limiting. In addition, it should be understood that the numerical ranges recited in the specification are intended to include every integer value within the range and every fraction within the range. Any smaller range within the range is also intended to be included. The upper and lower limits of the ranges are included in the range.

[0034] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In the case of conflict between the present specification and any document incorporated by reference, the present specification will control.

[0035] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples are illustrative only.

[0036] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having" or the like are open-ended expressions that are intended to denote the presence of stated features, items, elements, components, or the like but do not preclude the presence or addition of one or more other features, items, elements, components, or the like.

[0037] It should be noted that the present application does not describe in detail the conventional operation means in the art, and is not the focus of the present application.

[0038] The CeO2 used in the following examples and comparative examples of the present application was prepared by direct calcination: 42 g of Ce(NO3)3·6H2O was weighed into a mortar and ground thoroughly to a powder, then loaded into a crucible and placed in a muffle furnace, which was raised to 500℃ at a rate of 5℃ / min and maintained for 3 h, to obtain CeO2.

[0039] The agricultural lignin used was CAL, and the preparation steps of CAL were as follows: corn cob was subjected to hydrothermal pretreatment (hydrothermal pretreatment temperature was 180℃, time was 30 min) to degrade hemicellulose into xylo-oligosaccharide, then the hydrothermal residue was treated with dilute alkali solution (sodium hydroxide solution) for 30 min to obtain a residue rich in cellulose and a lignin solution, then the effluent (lignin solution) treated with alkali solution was adjusted to acidic conditions (pH = 2) to precipitate lignin, and the obtained lignin was combined. The purity of the obtained CAL was 94.42%, the weight average molecular weight was 3258 g / mol, the number average molecular weight was 2260 g / mol, and the polydispersity index was 1.44.

[0040] Methanol (purity 99.5%), isopropanol (purity 99.7%), ethyl acetate (purity 99.5%), hydrochloric acid (purity 37%), anhydrous ethanol (purity 99.5%), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, purity ≥98%) were purchased from Xilong Scientific Co., Ltd.; lanthanum nitrate hexahydrate (La(NO3)3·6H2O, purity ≥99%), citric acid monohydrate (purity 99%), vanillin (purity 99%), vanillic acid (purity 98%), p-hydroxybenzoic acid (purity 99%), ethylene glycol (purity 98%), potassium bromide (purity 99.5%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; syringaldehyde (purity ≥98%), syringic acid (purity ≥98%), p-hydroxybenzaldehyde (purity ≥98%), dodecane (purity >99%), deuterated dimethyl sulfoxide (purity 99.9%) were purchased from Shanghai Macklin Biochemical Co., Ltd.

[0041] Unless otherwise specified, all other raw materials used are commercially available products, and the source of these commercially available products does not affect the technical effect of this invention.

[0042] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0043] Example 1

[0044] (1) La(NO3)3·6H2O and Ni(NO3)2·6H2O were dissolved in water at room temperature and a stirring speed of 400 r / min to prepare La 3+ Ni 2+ Solution A, with a concentration of 0.06 mol / L;

[0045] (2) Dissolve citric acid in water at room temperature and a stirring speed of 400 r / min to prepare a solution B with a concentration of 0.144 mol / L;

[0046] (3) Mix 50 mL of solution A and 50 mL of solution B, then add 0.003 mol of ethylene glycol and 0.21 mol of CeO2 while stirring at 400 r / min and heating in a water bath at 80°C. Continue stirring until the solution becomes a transparent gel.

[0047] (4) The gel was dried at a constant temperature of 100℃ for 11h, and then ground in a mortar for 8min. Then it was placed in a muffle furnace and heated from room temperature to 400℃ at a heating rate of 3℃ / min and held for 2h. Then it was heated to 700℃ at a heating rate of 3℃ / min and held for 3h to obtain a LaNiO3 / CeO2 catalyst with a LaNiO3 loading of 5wt%.

[0048] The LaNiO3 / CeO2 catalyst prepared in this embodiment was applied to the catalytic oxidation of CAL to prepare aromatic aldehydes in an alkali-free system. The specific steps are as follows:

[0049] 1) CAL was dried at 105℃ for 6h beforehand, and then 1g CAL, 0.1g LaNiO3 / CeO2 catalyst, and 30mL isopropanol and water in a volume ratio of 1:1 were added to a 100mL micro reactor.

[0050] 2) Purge the inside of the vessel with nitrogen to remove air, then evacuate the vessel, and then introduce O2 at a pressure of 1 MPa. Heat the vessel from room temperature to 180°C at a reaction speed of 900 r / min and continue the reaction for 2 hours.

[0051] Example 2

[0052] (1) La(NO3)3·6H2O and Ni(NO3)2·6H2O were dissolved in water at room temperature and a stirring speed of 450 r / min to prepare La 3+ Ni2+ Solution A with concentration of 0.07 mol / L;

[0053] (2) Citric acid was dissolved in water to form solution B with concentration of 0.168 mol / L at room temperature and stirring speed of 450 r / min;

[0054] (3) 50 mL of solution A and 50 mL of solution B were mixed, then 0.0035 mol of ethylene glycol and 0.12 mol of CeO2 were added under stirring speed of 450 r / min and heating in water bath at 85°C, and the solution was stirred until it became transparent gel;

[0055] (4) The gel was dried at constant temperature of 105°C for 12 h, then ground in a mortar for 9 min. Then it was put into a muffle furnace, and heated at a heating rate of 3°C / min from room temperature to 450°C for 2.5 h, and then continued to be heated at a heating rate of 3°C / min to 750°C for 3.5 h, thus a LaNiO3 / CeO2 catalyst with LaNiO3 loading of 10 wt% was obtained.

[0056] The LaNiO3 / CeO2 catalyst prepared in this example was used as catalyst for CAL catalytic oxidation, and the application method was the same as that in Example 1.

[0057] Example 3

[0058] (1) La(NO3)3·6H2O and Ni(NO3)2·6H2O were dissolved in water to form solution A with concentration of 0.08 mol / L at room temperature and stirring speed of 400 r / min; 3+ , Ni 2+ Solution A with concentration of 0.08 mol / L;

[0059] (2) Citric acid was dissolved in water to form solution B with concentration of 0.192 mol / L at room temperature and stirring speed of 400 r / min;

[0060] (3) 50 mL of solution A and 50 mL of solution B were mixed, then 0.004 mol of ethylene glycol and 0.06 mol of CeO2 were added under stirring speed of 400 r / min and heating in water bath at 90°C, and the solution was stirred until it became transparent gel;

[0061] (4) The gel was dried at constant temperature of 100°C for 13 h, then ground in a mortar for 10 min. Then it was put into a muffle furnace, and heated at a heating rate of 3°C / min from room temperature to 400°C for 3 h, and then continued to be heated at a heating rate of 3°C / min to 700°C for 4 h, thus a LaNiO3 / CeO2 catalyst with LaNiO3 loading of 20 wt% was obtained.

[0062] The LaNiO3 / CeO2 catalyst prepared in this embodiment is used as a catalyst for CAL catalytic oxidation using the same method as in Example 1.

[0063] Example 4

[0064] (1) La(NO3)3·6H2O and Ni(NO3)2·6H2O were dissolved in water at room temperature and a stirring speed of 450 r / min to prepare La 3+ Ni 2+ Solution A, with a concentration of 0.06 mol / L;

[0065] (2) Dissolve citric acid in water at room temperature and stirring speed of 450 r / min to prepare solution B with a concentration of 0.144 mol / L;

[0066] (3) Mix 50 mL of solution A and 50 mL of solution B, then add 0.003 mol of ethylene glycol and 0.017 mol of CeO2 while stirring at 450 r / min and heating in a water bath at 80 °C. Continue stirring until the solution becomes a transparent gel.

[0067] (4) The gel was dried at a constant temperature of 105℃ for 11h, and then ground in a mortar for 8min. Then it was placed in a muffle furnace and heated from room temperature to 450℃ at a heating rate of 3℃ / min and held for 2h. Then it was heated to 750℃ at a heating rate of 3℃ / min and held for 3h to obtain a LaNiO3 / CeO2 catalyst with a LaNiO3 loading of 40wt%.

[0068] The LaNiO3 / CeO2 catalyst prepared in this embodiment is used as a catalyst for CAL catalytic oxidation using the same method as in Example 1.

[0069] Comparative Example 1 (LaNiO3 catalyst)

[0070] (1) La(NO3)3·6H2O and Ni(NO3)2·6H2O were dissolved in water at room temperature and a stirring speed of 400 r / min to prepare La 3+ Ni 2+ Solution A, with a concentration of 0.06 mol / L;

[0071] (2) Dissolve citric acid in water at room temperature and a stirring speed of 400 r / min to prepare a solution B with a concentration of 0.144 mol / L;

[0072] (3) Mix 50 mL of solution A and 50 mL of solution B, then add 0.003 mol of ethylene glycol while stirring at 400 r / min and heating in a water bath at 80°C, and add ammonia to adjust the pH to 8. Continue stirring until the solution becomes a transparent gel.

[0073] (4) The gel was dried at a constant temperature of 100°C for 11 h, and then ground in a mortar for 8 min. Subsequently, it was placed in a muffle furnace, and heated at a rate of 3°C / min from room temperature to 400°C for 2 h, and then continued to be heated at a rate of 3°C / min to 700°C for 3 h, to obtain the LaNi03catalyst.

[0074] The LaNi03catalyst prepared in the present comparative example was used as a catalyst in the method for applying CAL catalytic oxidation as in Example 1.

[0075] Comparative Example 2 (Ce02catalyst)

[0076] Ce02was used as the catalyst in the present comparative example.

[0077] The Ce02catalyst prepared in the present comparative example was used as a catalyst in the method for applying CAL catalytic oxidation as in Example 1.

[0078] The different loadings of LaNi03 / Ce02, LaNi03, and Ce02catalysts prepared in Examples 1-4 and Comparative Examples 1-2 were characterized and tested for performance, as follows:

[0079] Intrinsic properties of the different loadings of LaNi03 / Ce02, LaNi03, and Ce02catalysts prepared in Examples 1-4 and Comparative Examples 1-2:

[0080] X-ray diffraction (XRD, PuXi XRD-3X) was performed on a Bruker AXS D8 Focus diffractometer. The pattern was recorded with Cu-Ka radiation at a voltage of 40 kV and a current of 30 mA, scanning from 10° to 80° at a rate of 4° / min. α

[0081] Figure 1 Figure a is an XRD pattern of the different loadings of LaNi03 / Ce02, LaNi03, and Ce02prepared in Examples 1-4 and Comparative Examples 1-2. As can be seen from the figure, the LaNi03catalyst prepared is pure perovskite structure, and when LaNi03is loaded on the Ce02support, in addition to the LaNi03perovskite structure, a cubic crystal type Ce02phase also appears. In addition, as the loading increases from 5wt% to 40wt%, the diffraction peak of LaNi03is enhanced, while the diffraction peak of Ce02is weakened, indicating that LaNi03is successfully loaded on the Ce02support.

[0082] Raman was tested on a LabRAM HR Evolution instrument equipped with a 532 nm excitation wavelength. A three-grating monochromator with a charge-coupled detector was used to scan from 50 to 1800 cm-1.​-1 Signal acquisition is performed within the Raman shift range. The temperature is controlled below 0.1K.

[0083] Figure 1 Figure b shows the Raman spectra of LaNiO3 / CeO2, LaNiO3, and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2. From this figure, it can be seen that at 470 cm⁻¹... -1 The strong peaks shown are the vibrations of Ce-O bonds and the symmetric stretching mode (F). 2g (Related to) 470cm -1 The peak intensity at this point decreases as the LaNiO3 loading increases from 0 to 40 wt%. The strong peak disappears in LaNiO3, while it is strongest in CeO2, further demonstrating that LaNiO3 can be successfully loaded onto CeO2. (200 cm⁻¹) -1 The signal shown below is caused by the displacement of lanthanum ions, 417 cm⁻¹ -1 The location is due to the vibration of the oxygen octahedron at 390 cm. -1 The faint peak observed at the position is a characteristic shoulder peak of the Ni-O bond, while at 230 cm⁻¹... -1 The peak at that location is attributed to oxygen vacancies.

[0084] The characteristic structures of the LaNiO3 / CeO2, LaNiO3, and CeO2 catalysts with different loadings prepared in Examples 1–4 and Comparative Examples 1–2 were analyzed using a Fourier transform infrared spectroscopy (FTIR, PerkinElmer). Each sample was ground with KBr at a mass ratio of 1:100. The chromatography temperature was measured at 400–4000 cm⁻¹. -1 Record the spectrum within the wavenumber range with a resolution of 4 cm⁻¹. -1 Each sample was scanned 16 times.

[0085] Figure 1 Image c shows the FTIR spectra of LaNiO3 / CeO2, LaNiO3, and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2. It can be seen that at 560 cm⁻¹... -1 The peak observed is caused by metal-oxygen, which is due to the antisymmetric stretching vibration of the BO6 octahedral BO bond in ABO3 or related to the La-O stretching vibration. Furthermore, it also reflects the vibrational mode of the Ce-O bond, and the relationship between peak intensity and LaNiO3 loading is consistent with the FTIR results.

[0086] The surface area and pore size distribution of LaNiO3 / CeO2, LaNiO3, and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2 were measured using a Bestech BSD-PM1 instrument. The samples were degassed at 300 °C for 6 h at pressures between 5 μm Hg and 10 μm Hg for 10 s, and then subjected to N2 adsorption-desorption at 77 K. The BET specific surface area was obtained using an automated BET analyzer, and the pore size distribution was obtained using the Barrett-Joyner-Halenda (BJH) method.

[0087] Figure 2 In Figures a and b, N2 adsorption-desorption isotherms (a) and pore size distribution curves (b) of LaNiO3 / CeO2, LaNiO3, and CeO2 catalysts with different loadings prepared in Examples 1-4 and Comparative Examples 1-2 are shown. Figure 2 As can be seen from Figure a, the isotherm exhibits a type IV pattern within the P / P0 = 0.7–1 range. The low-pressure portion of the isotherm is almost linear, indicating that the constructed catalyst has a macroporous structure. With increasing relative pressure, an H3-type hysteresis loop appears within the P / P0 = 0.7–1 range, indicating the presence of mesoporous structures in the constructed catalyst. No adsorption saturation was observed in the high-pressure region of the isotherm, and the pore structure is irregular, exhibiting flat slits, cracks, wedges, etc. Figure 2 As can be seen from b, all six catalysts have a mixed porous structure, possessing macropores, mesopores, and micropores (mainly mesopores). Meanwhile, LaNiO3 exhibits the lowest adsorption capacity and the highest average pore size (42.6036 nm) (Table 1), but its specific surface area is the smallest (2.5410 m²). 2 / g. Conversely, CeO2 showed the highest adsorption capacity, the lowest average pore size (11.82 nm), and the largest specific surface area (51.4351 m²). 2 / g. The specific surface area increased slightly as the loading increased from 5 wt% to 20 wt%, but decreased significantly when the loading further increased to 40 wt%. This indicates that at lower loadings, the presence of LaNiO3 has little effect on the specific surface area of ​​CeO2 due to its good dispersibility. However, when the loading is too high, the aggregation of LaNiO3 particles leads to a decrease in specific surface area.

[0088] Table 1. Specific surface area and structural parameters of LaNiO3 / CeO2, LaNiO3, and CeO2 catalysts with different loadings.

[0089]

[0090]

[0091] In Table 1, a was obtained from BET results. b Micro-pore surface area and volume were calculated using t-plot method. c External surface area was calculated from total specific surface area minus micro-pore surface area. d Cumulative pore volume was obtained from BJH desorption. e Mesopore volume was obtained from total pore volume minus micro-pore volume. f Average pore diameter from BJH adsorption (4V / A). g Calculated from ICP.

[0092] In addition, the actual loading of LaNi03 in ICP results (Table 1) was closer to the theoretical value.

[0093] X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Fisher Scientific Escalab 250Xi system with Al K (1486.6 eV) radiation as excitation source and C1s (284.8 eV) as internal reference. Spectra were collected at ambient temperature and ultra-high vacuum. Core levels of La 3d, Ni 2p, Ce 3d, O1s species were recorded and their relative intensities were determined by curve fitting and integration of the deconvoluted signals in Gauss.

[0094] Figure 3 a-d are XPS spectra of La 3d (a), Ni 2p (b), Ce 3d (c) and O1s (d) of different loading of LaNi03 / Ce02, LaNi03, Ce02catalysts prepared in Example 1-4 and Comparative Example 1-2. From Figure 3 As can be seen from a of Table 2, La ions in the catalysts are mainly in +3 valence state. From Figure 3 As can be seen from b of Table 2, Ni 2p 1 / 2 From nothing to something, indicating that the loading of LaNi03 is indeed increasing, consistent with the EDS results. Figure 3 c is the XPS spectrum of Ce 3d orbit, when the loading of LaNi03 is 20wt%, Ce 3+ / Ce 4+ value is the highest, 0.38 (Table 3), indicating that the loading of LaNi03 leads to the enhancement of the interaction between LaNi03 and Ce02, more Ce 4+ is reduced to Ce 3+ , so that there are more Ce 3+ ions on the surface of the catalyst. As Figure 3 d and Table 4 show, the O ads / O lat value of both LaNi03 and Ce02 is low, the loading of LaNi03 makes the O ads / O lat value increase, indicating that the loading can improve the O ads / O lat The phenomenon again proved the synergistic effect between LaNiO3 and CeO2.

[0095] Table 2 Binding energy of La 3d orbit in different loading amount of LaNiO3 / CeO2, LaNiO3 catalyst

[0096]

[0097] Table 3 Binding energy of Ce 3d orbit in different loading amount of LaNiO3 / CeO2, CeO2 catalyst

[0098]

[0099] Table 4 Binding energy of O 1s orbit in different loading amount of LaNiO3 / CeO2, LaNiO3, CeO2 catalyst

[0100]

[0101] EPR was performed on BRUKE EMXPLUS instrument to detect the unpaired electron related to oxygen vacancy of the sample.

[0102] Figure 3 Figure 1e is the EPR spectrum of different loading amount of LaNiO3 / CeO2, LaNiO3, CeO2 catalyst prepared in Example 1-4 and Comparative Example 1-2. As shown in Figure 1e, there is a characteristic symmetrical peak at g = 2.003, which may be caused by oxygen vacancy. It is worth noting that the content of oxygen vacancy in LaNiO3 / CeO2 catalyst is higher than CeO2 or LaNiO3, which again proves the synergistic effect between LaNiO3 and CeO2. Figure 3 Temperature programmed reduction (H2-TPR) was performed on Microtrac BEL BELCAT instrument, first pre-treated with Ar at 250℃ for 60 min, then recorded data from 50℃ to 700℃ at 10℃ / min.

[0103]

[0104] Figure 2a is the H2-TPR, CO2 / NH3-TPD curve of different loading amount of LaNiO3 / CeO2, LaNiO3, CeO2 catalyst prepared in Example 1-4 and Comparative Example 1-2. From Figure 2a, it can be seen that, except for 20wt% LaNiO3 / CeO2 catalyst, the Ni Figure 4 Figure 4 3+ → Ni 2+ ​​The reduction temperatures of the peaks are all lower than that of LaNi03, which means that CeO2 as the support improves the redox performance of LaNi03 / CeO2. Also, except for 10wt% LaNi03 / CeO2, the Ni 2+ → Ni 0 and / or Ce 4+ → Ce 3+ The reduction temperatures of the peaks are all lower than that of LaNi03 and CeO2, which also means that the oxidation performance of LaNi03 / CeO2 catalyst is improved compared with single LaNi03 and CeO2, which again indicates the synergistic effect between them.

[0105] Table 5 H2-TPR semi-quantitative results of different loading LaNi03 / CeO2, LaNi03, CeO2 catalysts

[0106]

[0107] Temperature programmed desorption (CO2-TPD) was also performed on Microtrac BEL BELCAT chemisorption instrument. First, the sample was pretreated under 99.9% pure He (50 mL / min) at 250 °C for 60 min. Then, after cooling to 50 °C, CO2 / He mixture was adsorbed for 60 min, followed by He purging for 30 min, and finally, the signal was recorded by increasing the temperature to 700 °C at a rate of 10 °C / min.

[0108] Table 6 CO2-TPD semi-quantitative results of different loading LaNi03 / CeO2, LaNi03, CeO2 catalysts

[0109]

[0110] Figure 4 Figure 6 CO2-TPD curves of different loading LaNi03 / CeO2, LaNi03, CeO2 catalysts prepared in Examples 1-4 and Comparative Examples 1-2. From the figure, it can be seen that the CO2-TPD curves of LaNi03 / CeO2 catalysts are different from that of LaNi03 and CeO2, which means that the oxidation performance of LaNi03 / CeO2 catalyst is improved compared with single LaNi03 and CeO2, which again indicates the synergistic effect between them. Figure 4As can be seen from Table 6 and Figure 2c, the weak base site peak temperature of the four LaNi03 / Ce02 catalysts is higher than that of single LaNi03 or Ce02. However, the weak base site number of 40wt% LaNi03 / Ce02 is slightly less than that of Ce02, but much greater than that of LaNi03, but the peak temperature of the LaNi03 / Ce02 catalyst is the highest, the surface basicity is the strongest, which makes up for the defect of the slight lack of weak base sites. In addition, except for 40wt% LaNi03 / Ce02, the weak base site number of LaNi03 / Ce02 catalysts with loadings of 5wt%, 10wt% and 20wt% is greater than that of single LaNi03 or Ce02. At the same time, the number of medium base sites of LaNi03 after loading is more than that of single LaNi03 or Ce02, which is due to the strong oxygen storage and release capacity of Ce02, which helps to form more basic sites during the reaction.

[0111] The temperature programmed desorption (NH3-TPD) was also carried out on a Microtrac BEL BELCAT chemisorption instrument. First, the sample was pretreated at a temperature of 250°C for 60 min under a pure He (50 mL / min) with a purity of 99.9%. Then, after cooling to 50°C, NH2 / He mixed gas adsorption was switched for 60 min, followed by He purging for 30 min, and finally, the signal was recorded by increasing the temperature to 700°C at a rate of 10°C / min.

[0112] Figure 4 Figure 2c is the NH3-TPD curve of the different loadings of LaNi03 / Ce02, LaNi03 and Ce02 catalysts prepared in Examples 1-4 and Comparative Examples 1-2. As can be seen from Figure 2c and Table 7, the number and strength of acid sites change with the change of LaNi03 loading. When the LaNi03 loading is 5wt%, the total acid amount of the catalyst reaches 862.45 μmol / g, and the acid site density is 30.86 μmol / m2, which are the highest values under the experimental conditions. This phenomenon shows that an appropriate amount of LaNi03 can effectively enhance the total acid amount and acid site density of the Ce02 support. Figure 4 2 As can be seen from Figure 2c and Table 7, the number and strength of acid sites change with the change of LaNi03 loading. When the LaNi03 loading is 5wt%, the total acid amount of the catalyst reaches 862.45 μmol / g, and the acid site density is 30.86 μmol / m2, which are the highest values under the experimental conditions. This phenomenon shows that an appropriate amount of LaNi03 can effectively enhance the total acid amount and acid site density of the Ce02 support.

[0113] Table 7 NH3-TPD semi-quantitative results of different loadings of LaNi03 / Ce02, LaNi03 and Ce02 catalysts

[0114]

[0115] Gas chromatography mass spectrometry analysis of the bio-oil obtained by catalytic CAL oxidation of Examples 1-4 and Comparative Examples 1-2:

[0116] ​The liquid phase product obtained by the oxidation of CAL catalyzed by the catalysts of Examples 1-4 and Comparative Examples 1-2 was dissolved in ethyl acetate, and then the components were detected by GC-MS. The GC-MS test was performed by using an Agilent 5977A gas chromatograph-5975C mass spectrometer, wherein the chromatographic column for detecting aromatic aldehyde was HP-5MS (30 m x 0.25 mm x 0.25 μm), the injection amount was 1 μL, the temperature of the injection port, detector and interface was 280°C, and the temperature rising program was as follows: 60°C for 3 min; rising to 105°C at a rate of 5°C / min; rising to 105.5°C at a rate of 0.5°C / min; rising to 106°C at a rate of 0.1°C / min and maintaining for 2 min; rising to 115°C at a rate of 10°C / min; rising to 117°C at a rate of 0.2°C / min and maintaining for 1 min; rising to 127°C at a rate of 5°C / min; rising to 152°C at a rate of 10°C / min; rising to 156°C at a rate of 0.4°C / min and maintaining for 1 min; rising to 280°C at a rate of 40°C / min and maintaining for 2 min. The chromatographic column for detecting aromatic acid was HP-5MS (15 m x 0.25 mm x 0.25 μm), the injection amount was also 1 μL, the temperature of the injection port, detector and interface was 330°C, and the temperature rising program was as follows: maintaining at 60°C for 5 min; rising to 320°C at a rate of 20°C / min and maintaining for 5 min. The mass spectrometry ionization voltage was 70 eV, and the mass range was m / z 30-700.

[0117] Figure 5 The oxidation activity of the catalysts of different loadings of LaNiO3 / CeO2, LaNiO3 and CeO2 prepared for Examples 1-4 and Comparative Examples 1-2 without alkali catalyzing the oxidation of CAL is shown in the figure, wherein a is the conversion rate of CAL, b is the yield of liquid phase oil, c is the residue rate of solid phase product, and d is the yield of aromatic aldehyde acid. Figure 5 The experimental conditions were as follows: 30 mL of isopropyl alcohol-water (v / v = 1:1), 1.0 g of CAL, 0.1 g of catalyst, 1 MPa of O2, 180°C, 2 h (VLA, SYRAL, PHA, VLA, SYRA are vanillin, syringaldehyde, p-hydroxybenzoic acid, vanillic acid and syringic acid, respectively). It can be seen from Figure 5 that the conversion rate of LaNiO3 / CeO2 is significantly improved compared with single LaNiO3 or CeO2. In addition, the generation of liquid phase oil is promoted, and the formation of solid residue is inhibited. At the same time, when the loading is 20 wt%, Y aaThe highest yield of 8.62% was achieved at 20wt% loading. In addition, it was found that p-hydroxybenzoic acid (PHA), vanillic acid (VLA) and syringic acid (SYRA) were the main oxidation products. Furthermore, the highest yield of VLA was achieved at 20wt% loading, which was 2.67%. For SYRA, the highest yield was achieved at 10wt% loading, which was 2.21%. The yield of PHA showed a similar trend to that of VLA, i.e. the highest yield was achieved at 20wt% loading, which was 2.26%. In addition, the yield of each aromatic acid was higher than that without catalyst system or single LaNiO3 or CeO2 system. Overall, the highest yield of aromatic aldehyde acid was achieved at 20wt% loading, which was 8.62%.

[0118] Two-dimensional (2D) heteronuclear single quantum coherence (HSQC) correlated NMR spectroscopy was performed on a Bruker Advance 600MHz spectrometer. First, 100mg of CAL was dissolved in 0.5mL of DMSO-d6, which was then loaded into a NMR tube. The test conditions were as follows: 1 H 13 The relaxation time in the H dimension was 1.5s, the number of accumulations was 64, the number of sampling points was 1024, and the spectral width was 5000Hz. 1 The number of sampling points in the C dimension was 256, the spectral width was 18000Hz, and the carbon-hydrogen coupling constant was 145Hz. The solvent DMSO peak (δ 13 / δ C = 39.5 / 2.49) was used for chemical shift calibration. Data processing and plotting were performed using standard MestReNova. H

[0119] The proportions of the basic structural units and the content of β-0-4 linkages in CAL and its oxidized liquid phase oil are shown in Table 8. Table 8 Proportions of basic structural units and content of β-0-4 linkages in CAL and its oxidized liquid phase oil (% based on 100 C9 structural units)

[0120]

[0121] a S / G = 0.5 (S 2,6 +S' 2,6 ) / (G2+G'2);

[0122] b β-0-4 bond breaking rate = (content of β-0-4 bond in CAL - content of β-0-4 bond in liquid phase product) / content of β-0-4 bond in CAL.

[0123] Figure 6 ​The 2D HSQC NMR spectra of the liquid phase products obtained by catalytic oxidation of CAL without base catalysis were prepared for the 2D HSQC NMR spectra of CAL and the different loadings of LaNiO3 / CeO2, LaNiO3 and CeO2 catalysts prepared in Examples 1-4 and Comparative Examples 1-2.

[0124] As can be seen from Figure 6 It can be seen that the catalytic oxidation reactions of different catalysts mainly occur on the side chain of CAL, and the aromatic ring is not oxidized. In addition, in the non-catalyst system, the β-O-4 bond is only broken by 45.28%. In contrast, the use of catalysts greatly promotes the breaking of the β-O-4 bond, especially the breaking of the β-O-4 bond under CeO2 catalysis is the highest (86.15%). In addition, the breaking of the β-O-4 bond under catalysis is the highest (83.33%) when the loading of LaNiO3 in the supported LaNiO3 / CeO2 catalyst is 20wt%, which is slightly lower than that of CeO2 independent catalysis, but the yield of aromatic aldehyde acid obtained by catalytic oxidation of CAL without base catalysis by 20wt% LaNiO3 / CeO2 catalyst is higher than that of CeO2 independent catalysis. This is because CeO2 catalysis is more conducive to the breaking of the C α -C β -O-4 in C α -C β bond, thereby forming more aromatic acids, and the latter will further react with the alcohol solvent to form aromatic esters, ultimately leading to a decrease in the yield of aromatic aldehyde acid.

[0125] In summary, the LaNiO3 / CeO2 catalyst prepared in the present application has a synergistic catalytic effect and can efficiently break the β-O-4 bond of lignin, and is suitable for catalytic oxidation of CAL in an alkaline-free system to produce value-added aromatic aldehyde acid.

[0126] Each embodiment in the specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other.

[0127] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a catalyst for the production of aromatic aldehyde acid from agricultural lignin by alkali-free oxidation, characterized by, The method comprises the following steps: The lanthanum source and the nickel source are dissolved in water to form solution A; citric acid is dissolved in water to form solution B; the solution A, the solution B, CeO2 and ethylene glycol are mixed and reacted to obtain a gel; and the gel is dried, ground and calcined to obtain the agricultural lignin catalyst for the production of aromatic aldehyde acid by alkaline-free oxidation.

2. The production method according to claim 1, characterized by, The lanthanum source comprises La(NO3)3 and / or lanthanum acetate; and the nickel source comprises Ni(NO3)2 and / or nickel acetate.

3. The preparation method according to claim 1, characterized in that, The concentration of La 3+ and Ni 2+ in the solution A is independently 0.06-0.08 mol / L; and / or, the concentration of citric acid in the solution B is 0.144-0.192 mol / L; and / or, the ratio of the total molar amount of La 3+ and Ni 2+ to the molar amount of citric acid is 1:1.

2.

4. The method of claim 1, wherein, The La 3+ , Ni 2+ and ethylene glycol are in a molar ratio of 1:1:0.

5.

5. The preparation method according to claim 1, characterized in that, The reaction temperature is 80-90 DEG C; the drying temperature is 100-105 DEG C and the drying time is 11-13 h; the grinding time is 8-10 min; the calcination comprises two stages; the first stage is precalcination, the precalcination temperature is 400-450 DEG C, the temperature rising rate is 3 DEG C / min and the holding time is 2-3 h; the second stage temperature is 700-750 DEG C, the temperature rising rate is 3 DEG C / min and the holding time is 3-4 h.

6. The catalyst for the production of aromatic aldehyde acid by the non-alkali oxidation of agricultural lignin, which is prepared by the method according to any one of claims 1 to 5, characterized in that, The agricultural lignin catalyst for the production of aromatic aldehyde acid by alkaline-free oxidation is LaNiO3 / CeO2 catalyst, wherein the loading amount of LaNiO3 is 5-40 wt%.

7. The application of the LaNiO3 / CeO2 catalyst in the production of aromatic aldehyde acid by alkaline-free oxidation of agricultural lignin according to claim 6.

8. A method for producing aromatic aldehyde acid from agricultural lignin without alkali oxidation, characterized by, The method comprises the following steps: The agricultural lignin, the LaNiO3 / CeO2 catalyst and a co-solvent are mixed and reacted in an oxygen atmosphere to obtain aromatic aldehyde acid.

9. The method of claim 8, wherein, The co-solvent is composed of isopropyl alcohol and water, and the volume ratio of the isopropyl alcohol to water is 1:0-1; the amount ratio of the agricultural lignin, the LaNiO3 / CeO2 catalyst and the co-solvent is 0.5-1 g:0.1-0.4 g:20-30 mL.

10. The method of claim 8, wherein, The oxygen pressure is 0.4-1.0 MPa, the reaction time is 1-2 h and the reaction temperature is 120-200 DEG C.

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