阅读说明：本技术 一种MnAl-LDO固体酸及其应用 (MnAl-LDO solid acid and application thereof ) 是由 李勇飞 贺泽民 刘跃进 付琳 马秀文 邓文聪 于 2019-11-28 设计创作，主要内容包括：本发明公开一种MnAl-LDO固体酸,其制备成本低,催化活性高,稳定性好,可重复使用,用于五羟甲基糠醛催化氧化合成2,5-二甲酰基呋喃,当MnAl-LDO固体酸催化剂、反应原料五羟甲基糠醛、反应溶剂二甲亚砜的质量比为0.63～0.95:1:40～50,反应温度110～130℃,在通氧条件下反应4～6h,产物2,5-二甲酰基呋喃质量收率达86％。(The invention discloses a MnAl-LDO solid acid which is low in preparation cost, high in catalytic activity, good in stability and reusable, is used for synthesizing 2, 5-diformylfuran through catalytic oxidation of pentamethyl furfural, and when the mass ratio of a MnAl-LDO solid acid catalyst to reaction raw material pentamethyl furfural to reaction solvent dimethyl sulfoxide is 0.63-0.95: 1: 40-50, the reaction temperature is 110-130 ℃, the reaction is carried out for 4-6 hours under the condition of oxygen introduction, and the mass yield of the product 2, 5-diformylfuran reaches 86%.)

1. A MnAl-LDO solid acid is characterized in that:

the MnAl-LDO solid acid contains Mn and Al with a mol ratio of 1-4: 1, and the Mn and Al account for 20-30% of the MnAl-LDO solid acid in percentage by mass;

the MnAl-LDO solid acid is of an irregular sheet structure, the pore diameter of the MnAl-LDO solid acid is 5-10 nm, and the pore volume of the MnAl-LDO solid acid is 0.04-0.4 cm³A specific surface area of 78-118 m²/g；

The precursor of the MnAl-LDO solid acid is manganese-aluminum hydrotalcite which is prepared from Mn²⁺And Al³⁺Cationic hydroxyl laminates and CO₃ ^2-Anion, and crystal water hydrogen bonded with laminate by hydroxyl or interlayer anion exists between layers, and this characteristic structure makes Mn²⁺And Al³⁺The cations are uniformly distributed in the regular hydroxyl laminate, interlayer water and interlayer CO are removed by roasting₃ ^2-Anion, which makes the active component Mn in a highly dispersed state;

in the MnAl-LDO solid acid, Mn is 3d⁵4s²The special valence layer electronic configuration exists in all valence states from 0 to +7, Mn in different valence states can be mutually converted to generate strong redox characteristics, and after the manganese-aluminum hydrotalcite is roasted at 400-500 ℃, Al in an XRD spectrum of MnAl-LDO (rare earth metal oxide-rare earth oxide-low-dropout regulator)₂O₃In amorphous form, Mn in MnO₂、Mn₃O₄The crystal form exists, and no manganese-aluminum spinel oxide appears, which indicates that the structure of the MnAl-LDO does not collapse after roasting.

In the MnAl-LDO solid acid, Mn is Mn²⁺、Mn³⁺、Mn⁴⁺The valence of (2) exists, and as the ratio of Mn to Al is increased, part of Mn on the surface of the MnAl-LDO⁴⁺Quilt Mn³⁺The substitution causes a charge imbalance which is compensated by the creation of oxygen vacancies, Mn⁴⁺Or Mn³⁺The presence of lattice oxygen selectively oxidizes pentamethylomethylfurfural to 2, 5-diformylfuran, Mn⁴⁺Or Mn³⁺Is reduced to Mn³⁺Or Mn²⁺And then oxidizing and supplementing lattice oxygen by oxygen, thereby improving the storage capacity and the migration activity of the MnAl-LDO solid acid to active oxygen and ensuring that the MnAl-LDO solid acid has higher catalytic activity;

the MnAl-LDO solid acid is prepared by the following method: with Mn (NO)₃)₂、Al(NO₃)₃.9H₂O、Na₂CO₃And NaOH is used as a raw material, the molar ratio of the four raw materials is controlled to be 1-4: 1: 0.032-0.035: 0.09-0.11, a MnAl hydrotalcite-like precursor is prepared by adopting a coprecipitation method, and interlayer water and interlayer CO in the MnAl hydrotalcite-like precursor are calcined to ensure that interlayer water and interlayer CO in the MnAl hydrotalcite-like precursor₃ ^2-The anions are dissipated in a gas form, a porous MnAl-LDO with large specific surface area is left, meanwhile, due to the lattice positioning effect, the active component Mn in the MnAl-LDO laminate is still in a highly dispersed state in the roasting process, the migration and aggregation are not generated, the MnAl-LDO solid acid with large specific surface area and uniformly dispersed active centers is formed, and meanwhile, Al exists in the MnAl-LDO₂O₃Therefore, the MnAl-LDO solid acid has good thermal stability, and specifically comprises the following steps:

adding Mn (NO)₃)₂And Al (NO)₃)₃.9H₂Adding O into deionized water according to the molar ratio of Mn to Al of 1-4: 1, and stirring and dissolving at 25-37 ℃ to form a manganese aluminum nitrate mixed salt solution with the concentration of 0.16-0.66 mol/L; then weighing a certain amount of Na₂CO₃Stirring and dissolving NaOH at room temperature to respectively form 0.54-0.58 mol/L sodium carbonate and 1.65-1.68 mol/L sodium hydroxide solution; mixing manganese aluminum nitrate mixed salt solution with sodium hydroxide and sodium carbonate solution according to the volume ratio of 1:0.5 to EAnd 2, slowly adding the mixture into a reactor at the ratio of 0.3-1.2, mixing and stirring, controlling the pH value of the whole mixed solution to be 9-11, stirring at 60 ℃ for 30-60 min, aging at 80 ℃ for 24h to obtain a white solid precipitate, performing suction filtration and washing on the white solid precipitate by using deionized water until the pH value of filtrate is 7, drying a filter cake at 80-100 ℃ for 12h to obtain a manganese-aluminum hydrotalcite precursor, placing the manganese-aluminum hydrotalcite precursor into a muffle furnace, heating to 400-500 ℃ at the heating rate of 1-2 ℃/min, roasting for 4-6 h, and naturally cooling to obtain brown solid powder, namely the MnAl-LDO solid acid containing the manganese-aluminum composite metal oxide.

2. The method for synthesizing 2, 5-diformylfuran by using the MnAl-LDO solid acid as the catalyst to catalyze the selective oxidation of the pentamethyl furfural, which is characterized by comprising the following steps: the mass ratio of the MnAl-LDO solid acid catalyst to the reaction raw material of the pentamethyl furfural to the reaction solvent of dimethyl sulfoxide is 0.63-0.95: 1: 40-50, the reaction temperature is 110-130 ℃, the reaction is carried out for 4-6 hours under the condition of oxygen introduction, after the reaction is finished, the reaction product is cooled to room temperature, the reaction solvent is recovered, the lower layer catalyst is centrifugally separated out, the oxidation product of 2, 5-diformylfuran is obtained, the mass yield of the 2, 5-diformylfuran reaches 86%, the lower layer catalyst after centrifugal separation is precipitated, filtered, washed by ethyl acetate, dried at the constant temperature of 80-100 ℃ for 8-12 hours, and then the catalyst is reused for the next time.

Technical Field

The invention belongs to the field of biomass energy catalysis, and relates to MnAl-LDO solid acid, a preparation method thereof and application of the MnAl-LDO solid acid in catalytic oxidation of pentamethyl furfural to synthesis of 2, 5-diformylfuran.

Background

The biomass resource is used as a renewable organic carbon source which can replace resources such as coal, petroleum and the like and is used for producing fine chemicals, and becomes a research hotspot for development, wherein lignocellulose has the characteristics of low price, easy obtaining and rich storage capacity and becomes the most direct raw material source for developing and utilizing the biomass resource, 40-50% of components in the lignocellulose are cellulose, the cellulose consists of β -D pyran glucose, the cellulose is connected in series through β -1,4 glycosidic bonds, the polymerization degree is 100-20000, and multi-molecular glucose can be obtained after depolymerization.

Disclosure of Invention

Objects of the invention

The invention aims to provide a solid acid MnAl-LDO and a method for catalytically synthesizing 2, 5-diformylfuran by using the same.

Technical scheme of the invention

1. A MnAl-LDO solid acid is characterized in that:

the MnAl-LDO solid acid contains Mn and Al with a mol ratio of 1-4: 1, and the Mn and Al account for 20-30% of the MnAl-LDO solid acid in percentage by mass;

the MnAl-LDO solid acid is of an irregular sheet structure, the pore diameter of the MnAl-LDO solid acid is 5-10 nm, and the pore volume of the MnAl-LDO solid acid is 0.04-0.4 cm³A specific surface area of 78-118 m²/g；

The precursor of the MnAl-LDO solid acid is manganese-aluminum hydrotalcite which is prepared from Mn²⁺And Al³⁺Cationic hydroxyl laminates and CO₃ ^2-Anion, and crystals hydrogen-bonded to the laminate with hydroxyl groups or interlayer anionsWater, this characteristic structure being such that Mn is present²⁺And Al³⁺Cations are uniformly distributed in a regular hydroxyl laminate, and interlayer water and interlayer CO are removed by roasting at 400-500 DEG C₃ ^2-Anion, which makes the active component Mn in a highly dispersed state; in the XRD spectrum of MnAl-LDO, Al₂O₃In amorphous form, Mn in MnO₂、Mn₃O₄The crystal form exists, no manganese-aluminum spinel oxide appears, and the MnAl-LDO structure does not collapse after roasting

In the MnAl-LDO solid acid, Mn is Mn²⁺、Mn³⁺、Mn⁴⁺The valence of (2) exists, and as the ratio of Mn to Al is increased, part of Mn on the surface of the MnAl-LDO⁴⁺Quilt Mn³⁺The substitution causes a charge imbalance which is compensated by the creation of oxygen vacancies, Mn⁴⁺Or Mn³⁺The presence of lattice oxygen selectively oxidizes pentamethylomethylfurfural to 2, 5-diformylfuran, Mn⁴⁺Or Mn³⁺Is reduced to Mn³⁺Or Mn²⁺And then oxidizing and supplementing lattice oxygen by oxygen, thereby improving the storage capacity and the migration activity of the MnAl-LDO solid acid to active oxygen and ensuring that the MnAl-LDO solid acid has higher catalytic activity;

the MnAl-LDO solid acid is prepared by the following method: with Mn (NO)₃)₂、Al(NO₃)₃.9H₂O、Na₂CO₃And NaOH is used as a raw material, the molar ratio of the four raw materials is controlled to be 1-4: 1: 0.032-0.035: 0.09-0.11, a MnAl hydrotalcite-like precursor is prepared by adopting a coprecipitation method, and interlayer water and interlayer CO in the MnAl hydrotalcite-like precursor are calcined to ensure that interlayer water and interlayer CO in the MnAl hydrotalcite-like precursor₃ ^2-The anions are dissipated in a gas form, a porous MnAl-LDO with large specific surface area is left, meanwhile, due to the lattice positioning effect, the active component Mn in the MnAl-LDO laminate is still in a highly dispersed state in the roasting process, the migration and aggregation are not generated, the MnAl-LDO solid acid with large specific surface area and uniformly dispersed active centers is formed, and meanwhile, Al exists in the MnAl-LDO₂O₃Therefore, the MnAl-LDO solid acid has good thermal stability, and specifically comprises the following steps:

adding Mn (NO)₃)₂And Al (NO)₃)₃.9H₂Adding O into deionized water according to the molar ratio of Mn to Al of 1-4: 1, and stirring and dissolving at 25-37 ℃ to form a manganese aluminum nitrate mixed salt solution with the concentration of 0.16-0.66 mol/L; then weighing a certain amount of Na₂CO₃Stirring and dissolving NaOH at room temperature to respectively form 0.54-0.58 mol/L sodium carbonate and 1.65-1.68 mol/L sodium hydroxide solution; slowly adding the mixed solution of manganese aluminum nitrate and sodium hydroxide and sodium carbonate solution into a reactor according to the volume ratio of 1: 0.5-2: 0.3-1.2, mixing and stirring, controlling the pH value of the whole mixed solution to be 9-11, stirring at 60 ℃ for 30-60 min, aging at 80 ℃ for 24h to obtain a white solid precipitate, performing suction filtration and washing on the white solid precipitate by using deionized water until the pH value of the filtrate is 7, drying the filter cake at 80-100 ℃ for 12h to obtain a manganese aluminum hydrotalcite precursor, placing the manganese aluminum hydrotalcite precursor into a muffle furnace, heating to 400-500 ℃ at the heating rate of 1-2 ℃/min, roasting for 4-6 h, and naturally cooling to obtain brown solid powder, namely MnAl-LDO solid acid containing manganese aluminum composite metal oxide;

2. the method for synthesizing 2, 5-diformylfuran by selectively oxidizing the pentamethyl furfural by using the MnAl-LDO solid acid as the catalyst in the step 1 is characterized by comprising the following steps of: the mass ratio of the MnAl-LDO solid acid catalyst to the reaction raw material of the pentamethyl furfural to the reaction solvent of dimethyl sulfoxide is 0.63-0.95: 1: 40-50, the reaction temperature is 110-130 ℃, the reaction is carried out for 4-6 hours under the condition of oxygen introduction, after the reaction is finished, the reaction product is cooled to room temperature, the reaction solvent is recovered, the lower layer catalyst is centrifugally separated out, the oxidation product of 2, 5-diformylfuran is obtained, the yield of the 2, 5-diformylfuran reaches 86%, the lower layer catalyst after centrifugal separation is precipitated, filtered, washed by ethyl acetate, dried at the constant temperature of 80-100 ℃ for 8-12 hours, and then the catalyst is repeatedly used for the next time.

Technical features and effects of the invention

1. The preparation process of the solid acid MnAl-LDO is simple, firstly, the manganese-aluminum hydrotalcite precursor with the layered structure is prepared, and the porous flaky solid acid MnAl-LDO with uniformly and stably distributed acid active sites and large specific surface area can be obtained by roasting the precursor at 450 ℃.

2. The MnAl-LDO solid acid is prepared by using the manganese nitrate as a manganese source, and has the advantages of low preparation cost, high catalytic activity, good stability and repeated use.

Preparing 2, 5-diformylfuran by catalyzing 5-hydroxymethylfurfural with MnAl-LDO solid acid, reacting for 4-6 hours at the reaction temperature of 110-130 ℃ under the condition of introducing oxygen in the mass ratio of the MnAl-LDO solid acid catalyst to the reaction raw material of the pentamethylfurfural to the reaction solvent of dimethyl sulfoxide of 0.63-0.95: 40-50, and cooling to room temperature after the reaction is finished to obtain the oxidation product 2, 5-diformylfuran with the mass yield of 86%

Mn as Mn in MnAl-LDO solid acid²⁺、Mn³⁺、Mn⁴⁺The valence being present, and Mn⁴⁺Or Mn³⁺The presence of lattice oxygen allows selective oxidation of the pentamethylomethylfurfural to 2, 5-diformylfuran, while Mn⁴⁺Or Mn³⁺Is reduced to Mn³⁺Or Mn²⁺And then oxidizing and supplementing lattice oxygen by oxygen to ensure that the MnAl-LDO solid acid has higher catalytic activity.

Drawings

FIG. 1 shows an SEM topography of MnAl-LDO. From the graph (a), it can be seen that the products of the manganese aluminum hydrotalcite-like compounds all exhibit a network-like porous structure after calcination, which is caused by the pores formed by the interparticle interconnections. It is further shown by the higher resolution of the topography (b) that the particle basis is a sheet-like structure of some irregular polygons.

FIG. 2 shows XRD patterns of MnAl-LDO with different Mn/Al ratios, wherein the Mn/Al ratios of a, b, c and d are 1:1, 2:1, 3:1 and 4:1, respectively, and the peaks at 18.41 °, 29.27 °, 32.72 °, 36.52 °, 44.87 °, 51.12 °, 54.31 °, 56.21 °, 58.71 °, 60.32 ° and 65.01 ° are attributed to Mn₃O₄The peaks at 31.64 DEG and 38.48 DEG corresponding to the crystal planes of (101), (112), (103), (211), (220), (105), (312), (303), (321), (224) and (400) are summarized as MnO₂The crystal planes correspond to (200) and (004), respectively. It is seen from the figure that the diffraction peak becomes smaller as the manganese-aluminum ratio increases, since the increase in Mn content decreases the crystallinity and order of the sampleLow, in addition no Al appears₂O₃Characteristic peaks of the crystal phase, indicating Al in MnAl-LDO₂O₃Existing in an amorphous form, when the manganese-aluminum ratio is 3:1, the catalytic reaction effect is best, and the catalytic reaction effect is almost unchanged when the manganese-aluminum ratio is increased, so that the relation between the MnAl-LDO catalytic effect and the crystallinity of the MnAl-LDO is not large, and Mn is mainly used³⁺、Mn⁴⁺The content and the acidity of the MnAl-LDO.

FIG. 3 shows that XPS is used to detect the valence information of MnAl-LDO elements, and FIG. 3a shows that the XPS spectrum of Mn 2p has two main peaks, and the binding energies 642e V and 653e V correspond to Mn 2p respectively_3/2、Mn 2p_1/2. Adding Mn 2p_3/2The fitting peak is divided into three characteristic peaks, and the binding energies of 641.6e V, 643.1e V and 645.0e V respectively correspond to Mn³⁺、Mn⁴⁺、Mn³⁺The satellite peak of (a). FIG. 3b shows that the peak of Al 2p3/2 is concentrated in 70-78eV, corresponding to Al³⁺The satellite peak of (a). And Mn⁴⁺And Al³⁺Can provide acid sites, which are favorable for the adsorption of the MnAl-LDO to the pentamethol furfural, Mn⁴⁺Or Mn³⁺The presence of lattice oxygen allows selective oxidation of the pentahydroxymethylfurfural to 2, 5-diformylfuran while inhibiting reaction transition oxidation to furandicarboxylic acid.

FIGS. 4a and b are NH before and after the calcination of MnAl-LDO, respectively₃-TPD. The MnAl-LDO surface before roasting mainly has medium acidity sites, and the peak position of the MnAl-LDO surface is between 300 ℃ and 500 ℃. The surface of the MnAl-LDO after being roasted has weak acidity site (peak position is between 100 ℃ C. and 300 ℃ C.), medium acidity site (peak position is between 300 ℃ C. and 500 ℃ C.) and strong acidity site (peak position is between 500 ℃ C. and 800 ℃ C.). This indicates the presence of MnO in the calcined MnAl-LDO₂，Mn₃O₄And Al₂O₃Respectively correspond to Mn⁴⁺、Mn³⁺And Al³⁺In which Mn is⁴⁺And Al³⁺The acidity site is provided, so that the acidity of the MnAl-LDO is enhanced, and the adsorption of the pentamethyl furfural is facilitated, while the Mn⁴⁺Or Mn³⁺The presence of lattice oxygen allows selective oxidation of the pentamethylomethylfurfural to 2, 5-diformylfuran, while Mn⁴⁺Or Mn³⁺Is reduced to Mn³⁺Or Mn²⁺Then lattice oxygen is supplemented by oxidation of oxygen,thereby enhancing the activity of the catalyst.

Detailed Description

The technical means and the mode of carrying out the present invention will be described below by way of examples, but the technical means and the mode of carrying out the present invention are not limited to the following examples.