Preparation method and application of Fe / Fe3C-MOR core-shell structure catalyst for catalytically depolymerizing lignin

Abstract

The invention relates to the technical field of iron-based catalysts, in particular to a preparation method and application of a Fe / Fe3C-MOR core-shell structure catalyst for catalytic depolymerization of lignin, and the preparation method comprises the following steps: adding ferric sodium ethylene diamine tetraacetate into deionized water, stirring and dissolving to obtain a yellowish-brown transparent solution to obtain an EDTA-Fe and Na solution; the preparation method comprises the following steps: adding commercial mordenite into an EDTA-Fe and Na solution, uniformly mixing, heating and stirring in a constant-temperature water bath at 60-70 DEG C for 4 hours, evaporating deionized water at 80-90 DEG C, drying in a drying oven at 105 DEG C overnight, grinding, and sieving with a 80-mesh sieve to obtain solid powder; and putting the obtained solid powder into a tubular calcining furnace, heating to 700 DEG C in a reducing gas atmosphere, calcining at a constant temperature, and cooling to room temperature to obtain the Fe / Fe3C-MOR core-shell structure catalyst. The Fe / Fe3C-MOR core-shell structure catalyst prepared by the method can efficiently catalyze and depolymerize lignin to directionally and selectively generate phenol monomers, the selectivity can be higher than 70%, and the stability is high.

Description

Technical Field

[0001] The present invention relates to the technical field of iron-based catalysts, and particularly relates to a preparation method and application of an Fe / Fe 3 C-MOR core-shell structure catalyst for catalytic depolymerization of lignin. Background Art

[0002] Lignin is one of the main components of lignocellulosic biomass and a renewable source rich in aromatic polymers. Depolymerizing lignin into liquid fuels is a formidable challenge in the field of renewable energy. In particular, the efficient depolymerization of lignin into liquid fuels with directional selectivity is a technology that needs to be breakthrough. Metal catalysts are a special solid-phase catalyst composed of metal nanoparticles and a carrier, with high catalytic activity and catalytic selectivity, and are widely used in chemical reactions such as hydrogenation reactions, oxidation reactions, and alkylation reactions. Precious metals exhibit unique lignin conversion rates due to their special electronic structures and relatively high active metal surfaces. For example, the invention patent with the application number CN 202211625710 4 discloses a method for preparing cellulose and lignin oil by depolymerizing lignocellulose without exogenous hydrogen. The catalyst includes a carrier and an active ingredient supported on the carrier, and the active ingredient is selected from at least one of platinum, palladium, ruthenium, nickel, and their alloys. Due to the high price and scarce reserves of precious metals, in recent years, extensive research has been conducted on metal catalysts such as transition metals Ni, Co, Mo, Fe, etc. For example, the invention patent with the application number CN202310566911.X discloses a preparation method of a molybdenum carbide hydrogenolysis lignin catalyst, in which the transition metal atoms are stably embedded in the acid-etched C vacancies, effectively promoting catalytic activity and realizing the oxidative depolymerization of C-O bonds and stubborn C-C bonds. The transition metal and MOR zeolite promote an increase in acidic sites. For example, the invention patent with the application number CN 117361556 A discloses a method for preparing Fe-MOR zeolite molecular sieve by solid-phase method based on fly ash and its application. The introduction of transition metal Fe makes the MOR zeolite molecular sieve have more acidic sites (medium-strong acid sites, strong acid sites). The increase in acidic sites is beneficial to providing protons, and at the same time, the catalyst has a strong adsorption effect.

[0003] Previously, the inventors have conducted extensive research in the field of lignin catalytic depolymerization and have published many relevant papers and patent documents at home and abroad. For example, the literature "Catalytic depolymerization of kraft lignin for liquid fuels and phenolic monomers over molybdenum-based catalysts: The effect of supports", as well as the authorized invention patents CN202111672123.6 (a nickel-cerium biochar catalyst and its preparation method and application), CN202110249761.0 (an iron-sodium carbon material catalyst and its preparation method and application), CN202210304642.5 (a molybdenum carbide particle size-dependent nitrogen-doped carbon material catalyst and its preparation method and application), and CN202310144507.3 (a cobalt-zirconium / sepiolite catalyst and its preparation method and application). After years of in-depth research in the field of catalysts by the inventors, it has been found that when iron-based catalysts are used for the catalytic depolymerization of lignin, the selectivity of phenolic monomers is generally lower than 70% and the conversion rate of lignin is also generally lower than 90%. To further improve the conversion efficiency of iron-based catalysts for lignin and the yield of the target product phenolic monomers, the inventors have further developed a new type of metal catalyst Fe / Fe 3 C-MOR and applied it to the directional catalytic depolymerization of lignin. By loading Fe / Fe 3 C catalyst on mordenite rich in Bronsted acid and Lewis acid, the conversion rate of lignin and the selectivity of phenolic monomers are improved. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a preparation method and application of an Fe / Fe 3 C-MOR core-shell structure catalyst for catalytic depolymerization of lignin. Using an EDTA-Fe,Na solution and commercial MOR to synthesize an Fe / Fe 3 C-MOR metal catalyst provides a new idea for the efficient directional depolymerization of lignin to produce phenolic monomer compounds.

[0005] Based on the above purpose, the present invention provides a preparation method of an Fe / Fe 3 C-MOR core-shell structure catalyst for catalytic depolymerization of lignin, comprising the following steps:

[0006] (1) Add sodium iron ethylenediaminetetraacetate to deionized water and stir to dissolve it into a yellowish-brown transparent solution to obtain an EDTA-Fe,Na solution;

[0007] (2) Add commercial mordenite into the EDTA-Fe,Na solution. After uniform mixing, heat and stir in a constant temperature water bath at 60 - 70 °C for 4 h. After evaporating deionized water at 80 - 90 °C, dry overnight in an oven at 105 °C, grind, and pass through an 80-mesh sieve to obtain solid powder;

[0008] (3) Load the obtained solid powder into a tubular calcination furnace. Under a reducing gas atmosphere, heat up to 700 °C and keep it calcined at a constant temperature. After cooling to room temperature, Fe / Fe 3 C-MOR core-shell structure catalyst is obtained.

[0009] Furthermore, the dosage ratio of sodium iron(III) ethylenediaminetetraacetate, deionized water, and commercial mordenite is 0.2 - 0.8 g:50 mL:0.2 g - 0.8 g.

[0010] Furthermore, step (3) is specifically: Load the obtained solid substance into a tubular calcination furnace. Under an N 2 :H 2 = 9:1 reducing gas atmosphere, introduce it into the tubular furnace at a gas flow rate of 50 - 100 mL / min, and heat up to 700 °C at a rate of 4 °C / min, then keep it calcined at a constant temperature for 4 h, and cool to room temperature.

[0011] The present invention also provides the application of the Fe / Fe 3 C-MOR core-shell structure catalyst obtained by the preparation method in the catalytic depolymerization of lignin to selectively generate phenolic monomer compounds with high selectivity.

[0012] Furthermore, the method of the application is: Add raw material lignin and Fe / Fe 3 C-MOR catalyst into absolute ethanol, put it into a batch high-temperature and high-pressure reaction kettle, carry out the reaction under an inert gas, stir at a rotation speed of 400 - 500 r / min for 20 - 50 min, under the conditions of a temperature of 270 °C - 310 °C and a pressure of 6.5 - 8.5 MPa, keep the temperature for reaction for 3 - 4 h. After the reaction is completed, lower the temperature of the reaction kettle below 250 °C, then place it in an ice-water bath for rapid cooling treatment. After cooling to room temperature, filter by suction, and perform vacuum rotary evaporation to obtain lignin oil.

[0013] Furthermore, the inert gas is high-purity argon or high-purity nitrogen.

[0014] Furthermore, the dosage ratio of the lignin, Fe / Fe 3 C-MOR catalyst, and absolute ethanol is 0.99 - 1.01 g:0.19 - 0.21 g:30 mL.

[0015] Furthermore, the temperature of the vacuum rotary evaporation is 40 - 47 °C and the rotation speed is 65 - 95 r / min.

[0016] Furthermore, the raw material lignin is one or more of proto-lignin, alkali lignin, and sulfonate lignin.

[0017] Advantages of the present invention:

[0018] In the present invention, sodium iron(III) ethylenediaminetetraacetate is used as the active metal iron and carbon precursor, and commercial MOR is used as the carrier. Under a reducing atmosphere of H 2 / N 2 = 1:9, a core-shell structured catalyst with an Fe-C phase as the shell and MOR as the core is sintered. This novel Fe / Fe 3 C-MOR catalyst can catalytically depolymerize lignin to selectively generate phenol monomers with high selectivity, and its selectivity can be higher than 96.49%, and the conversion rate of lignin can be as high as 78.80%.

[0019] The Fe / Fe 3 C-MOR catalyst prepared in the present invention utilizes the active metal Fe to promote the generation of more Brønsted acid and Lewis acid active sites on MOR, and utilizes the Brønsted acid and Lewis acid active sites of MOR and the Fe / Fe 3 C metal active sites to synergistically reduce the activation energies of C-C and C-O bonds, realizing the selective polarization and cleavage of the C-C bonds and stubborn C-C bonds of lignin by the catalyst, and also promoting the cleavage of β-O-4 bonds. Under the action of supercritical ethanol medium, the in-situ hydrogen generated by the activation of metal sites promotes the hydrogenation of intermediates, realizing the alkylation of active monomers, and then inactivating the active monomers to avoid their re-polymerization to form oligomers at high temperatures, thereby increasing the conversion rate of phenol monomers to obtain more high-value-added monomers. This may also be the key reason for the directional catalytic depolymerization of lignin to generate phenol monomer compounds. At the same time, under the sintering conditions in a reducing gas atmosphere, a large number of oxygen vacancies are formed on the surface of the Fe / Fe 3 C-MOR catalyst, and the doping of Fe causes the structure of MOR to be damaged, forming a crystal SiO 2 structure, making its surface loaded with Fe / Fe 3 C to form a core-shell structure. The design of a large number of oxygen vacancies on the surface and the core-shell structure of the Fe-C phase also helps to improve the adsorption of lignin molecules by the catalyst and the effective contact between the active catalytic components and lignin. In addition, the increase in the content of EDTA-Fe,Na also improves the conductivity of the catalyst, and the higher electron cloud density on its surface may help to adsorb and activate lignin molecules and promote electron transfer during the reaction process, thereby promoting the cracking reaction and improving the lignin depolymerization efficiency.

[0020] The Fe / Fe 3The C-MOR catalyst has the characteristics of high stability and simple preparation process. It also has excellent charge transfer effect, which promotes the decomposition of ethanol into hydrogen radicals and alkyl radicals. By the surface activity of the catalyst, the C-C bond and stubborn C-O bond are broken, enabling the occurrence of hydrodeoxygenation reaction and alkylation reaction. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 For Example 3, the TEM characterization diagram of the Fe / Fe 3 C-MOR catalyst;

[0023] Figure 2 For Examples 1-4, the XRD characterization diagram of the Fe / Fe 3 C-MOR catalyst. Detailed Embodiments

[0024] To make the purpose, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in conjunction with specific embodiments.

[0025] The present invention provides a preparation method of an Fe / Fe 3 C-MOR core-shell structure catalyst for catalytic depolymerization of lignin, including the following steps:

[0026] (1) Add sodium ferric ethylenediaminetetraacetate to deionized water, stir and dissolve it into a yellowish-brown transparent solution to obtain an EDTA-Fe,Na solution;

[0027] (2) Add commercial mordenite to the EDTA-Fe,Na solution, mix evenly, then heat and stir in a constant temperature water bath at 60-70 °C for 4 h. After evaporating the deionized water at 80-90 °C, dry it overnight in an oven at 105 °C, grind it, and pass through an 80-mesh sieve to obtain a solid powder;

[0028] The dosage ratio of the sodium ferric ethylenediaminetetraacetate, deionized water, and commercial mordenite is 0.2-0.8 g:50 mL:0.2 g-0.8 g;

[0029] (3) Load the obtained solid powder into a tubular calcination furnace, and in N 2 :H 2In a reducing gas atmosphere with a ratio of 9:1, it is introduced into a tubular furnace at a gas flow rate of 50 - 100 mL / min, and heated to 700 °C at a rate of 4 °C / min, then calcined at a constant temperature for 4 h. After cooling to room temperature, Fe / Fe 3 C-MOR core-shell structure catalyst is obtained.

[0030] The present invention also provides the Fe / Fe 3 application of the C-MOR core-shell structure catalyst obtained by the preparation method in the catalytic depolymerization of lignin to selectively generate phenolic monomer compounds with high selectivity. The method of the application is as follows: Add the raw lignin and Fe / Fe 3 C-MOR catalyst into absolute ethanol, put it into a batch high-temperature and high-pressure reactor, and carry out the reaction under an inert gas of high-purity argon or high-purity nitrogen. Stir at a rotation speed of 400 - 500 r / min for 20 - 50 min. Under the conditions of a temperature of 270 °C - 310 °C and a pressure of 6.5 - 8.5 MPa, keep the temperature for reaction for 3 - 4 h. After the reaction, lower the temperature of the reactor to below 250 °C, then place it in an ice-water bath for rapid cooling. After cooling to room temperature, filter by suction, and under the conditions of a temperature of 40 - 47 °C and a rotation speed of 65 - 95 r / min, perform vacuum rotary evaporation to obtain lignin oil;

[0031] The dosage ratio of the lignin, Fe / Fe 3 C-MOR catalyst, and absolute ethanol is 0.99 - 1.01 g: 0.19 - 0.21 g: 30 mL;

[0032] The raw lignin is one of various lignins such as native lignin, alkali lignin, and sulfonate lignin.

[0033] Example 1

[0034] A preparation method of an Fe / Fe 3 C-MOR catalyst for catalytic depolymerization of lignin, comprising the following steps:

[0035] (1) Add 0.2 g of sodium iron(III) ethylenediaminetetraacetate to 50 mL of deionized water, stir and dissolve to form a yellow-brown transparent solution to obtain an EDTA-Fe,Na solution;

[0036] (2) Add 0.8 g of commercial mordenite to the EDTA-Fe,Na solution obtained in step (1), after uniform mixing, heat and stir in a constant temperature water bath at 70 °C for 4 h, evaporate the deionized water at 90 °C, then dry overnight in an oven at 105 °C, grind, and pass through an 80-mesh sieve to obtain a solid powder;

[0037] (3) Load the obtained solid powder into a tubular calcination furnace, in N 2 :H 2In a reducing gas atmosphere with a ratio of 9:1, it is introduced into a tubular furnace at a gas flow rate of 100 mL / min, heated to 700 °C at a rate of 4 °C / min, and calcined at a constant temperature for 4 h. After cooling to room temperature, Fe / Fe 3 C-MOR core-shell structure catalyst is obtained.

[0038] Using the obtained Fe / Fe 3 C-MOR catalyst to catalyze the depolymerization of lignin: 0.9975 g of sulfonated lignin and 0.1997 g of Fe / Fe 3 C-MOR catalyst are added to 30 mL of absolute ethanol, and then placed in a 100 mL batch high-temperature and high-pressure reactor. Under the protection of high-purity nitrogen, it is stirred at a speed of 480 r / min for 30 min, and then under the conditions of a temperature of 290 °C and a pressure of 7.5 MPa, a supercritical ethanol system is formed, and the reaction is carried out for 3 h. After the reaction is completed, the temperature of the reactor is lowered to 250 °C, and the reactor is placed in an ice-water bath for rapid cooling. After cooling to 25 °C at room temperature, it is filtered by suction, and under the conditions of a temperature of 46 °C and a rotation speed of 75 r / min, the obtained filtrate is vacuum rotary evaporated to remove absolute ethanol to obtain a liquid-phase product.

[0039] The Fe / Fe obtained in Example 1 3 C-MOR catalyst is subjected to X-ray diffraction, and it can be seen that Fe and Fe are loaded on the surface of the catalyst 3 C phase, while retaining the structural characteristics of mordenite. The Bronsted acid and Lewis acid sites contained on its surface synergistically promote the depolymerization of lignin with the active metal.

[0040] The Fe / Fe prepared through Example 1 3 C-MOR catalyst is subjected to BET analysis, and it can be seen that the surface of the catalyst has a large number of microporous structures, has a good adsorption effect on lignin, and promotes the catalytic depolymerization of lignin.

[0041] Example 2

[0042] A preparation method of an Fe / Fe 3 C-MOR catalyst for catalyzing the depolymerization of lignin, comprising the following steps:

[0043] (1) Add 0.4 g of sodium iron ethylenediaminetetraacetate to 50 mL of deionized water, stir and dissolve it into a yellow-brown transparent solution to obtain an EDTA-Fe,Na solution;

[0044] (2) Add 0.6 g of commercial mordenite to the EDTA-Fe,Na solution obtained in step (1), mix evenly, then heat and stir in a constant temperature water bath at 70 °C for 4 h, evaporate the deionized water at 90 °C, dry it overnight in an oven at 105 °C, grind it, and pass through an 80-mesh sieve to obtain a solid powder;

[0045] (3) Load the obtained solid powder into a tubular calcination furnace, and under a reducing gas atmosphere of N 2 :H 2 = 9:1, introduce it into the tubular furnace at a gas flow rate of 100 mL / min, and heat it to 700 °C at a rate of 4 °C / min, and then keep it at a constant temperature for calcination for 4 h. After cooling to room temperature, the Fe / Fe 3 C-MOR core-shell structure catalyst is obtained.

[0046] Use the obtained Fe / Fe 3 C-MOR catalyst to catalyze the depolymerization of lignin: Add 1.0012 g of sulfonate lignin and 0.2034 g of Fe / Fe 3 C-MOR catalyst into 30 mL of absolute ethanol, and then put it into a 100 mL batch high-temperature and high-pressure reactor. Under the protection of high-purity nitrogen, stir it at a speed of 480 r / min for 40 min, and then at a temperature of 290 °C and a pressure of 7.5 MPa, form a supercritical ethanol system, and react for 3 h. After the reaction is completed, lower the temperature of the reactor to 250 °C, place the reactor in an ice-water bath for rapid cooling, and after cooling to 25 °C at room temperature, filter it, and then under the conditions of a temperature of 46 °C and a speed of 75 r / min, vacuum rotary evaporate the obtained filtrate to remove absolute ethanol to obtain a liquid-phase product.

[0047] Perform X-ray diffraction on the Fe / Fe 3 C-MOR catalyst obtained in Example 2, and it can be seen that Fe and Fe 3 C phases are loaded on the surface of the catalyst. At this time, the mordenite structure breaks and forms a crystal SiO 2 structure.

[0048] Perform BET analysis on the Fe / Fe 3 C-MOR catalyst prepared in Example 2, and it can be seen that a large number of microporous structures are formed on the surface of the catalyst, which has a good catalytic effect on the depolymerization of lignin.

[0049] Example 3

[0050] A preparation method of an Fe / Fe 3 C-MOR catalyst for catalyzing the depolymerization of lignin, comprising the following steps:

[0051] (1) Add 0.6 g of sodium iron ethylenediaminetetraacetate to 50 mL of deionized water, stir and dissolve it into a yellow-brown transparent solution to obtain an EDTA-Fe,Na solution;

[0052] (2) Add 0.4 g of commercial mordenite to the EDTA-Fe,Na solution obtained in step (1). After uniform mixing, heat and stir in a constant temperature water bath at 70 °C for 4 h. After evaporating the deionized water at 90 °C, dry it overnight in an oven at 105 °C, grind it, and pass through an 80-mesh sieve to obtain a solid powder;

[0053] (3) Load the obtained solid powder into a tubular calcination furnace. Under a reducing gas atmosphere of N 2 :H 2 = 9:1, introduce it into the tubular furnace at a gas flow rate of 100 mL / min, and heat it to 700 °C at a rate of 4 °C / min, and keep it calcined at a constant temperature for 4 h. After cooling to room temperature, the Fe / Fe 3 C-MOR core-shell structure catalyst is obtained.

[0054] Use the obtained Fe / Fe 3 C-MOR catalyst to catalyze the depolymerization of lignin: Add 1.0004 g of sulfonated lignin and 0.2006 g of Fe / Fe 3 C-MOR catalyst to 30 mL of absolute ethanol, then put it into a 100 mL batch high-temperature and high-pressure reaction kettle. Under the protection of high-purity nitrogen, stir at a speed of 480 r / min for 40 min, and then form a supercritical ethanol system at a temperature of 290 °C and a pressure of 7.5 MPa. React for 3 h. After the reaction, cool the temperature of the reaction kettle to 250 °C, place the reaction kettle in an ice-water bath for rapid cooling, and after cooling to 25 °C at room temperature, filter it, and then vacuum rotary evaporate the obtained filtrate at a temperature of 46 °C and a speed of 75 r / min to remove absolute ethanol to obtain a liquid-phase product.

[0055] Through the TEM analysis and testing of the Fe / Fe 3 C-MOR catalyst prepared in Example 3, it can be seen that the surface of the catalyst has Fe and Fe 3 C phases, forming a silicon-supported Fe / Fe 3 C core-shell catalyst.

[0056] Perform X-ray diffraction on the Fe / Fe 3 C-MOR catalyst obtained in Example 3. It can be seen that the surface of the catalyst is loaded with Fe and Fe 3 C phases. At this time, the mordenite structure breaks and forms a crystal SiO 2 structure.

[0057] Through the BET analysis of the Fe / Fe 3 C-MOR catalyst prepared in Example 3, it can be seen that a large number of microporous structures are formed on the surface of the catalyst, which has a good adsorption effect on lignin and promotes the catalytic depolymerization of lignin.

[0058] Example 4

[0059] A preparation method of Fe / Fe 3 C-MOR catalyst for catalytic depolymerization of lignin, comprising the following steps:

[0060] (1) Add 0.8 g of sodium iron(III) ethylenediaminetetraacetate to 50 mL of deionized water, stir and dissolve to form a yellow-brown transparent solution to obtain an EDTA-Fe,Na solution;

[0061] (2) Add 0.2 g of commercial mordenite to the EDTA-Fe,Na solution obtained in step (1), after uniform mixing, heat and stir in a constant temperature water bath at 70 °C for 4 h, evaporate the deionized water at 90 °C, dry overnight in an oven at 105 °C, grind, and pass through an 80-mesh sieve to obtain a solid powder;

[0062] (3) Load the obtained solid powder into a tubular calcination furnace, and in a reducing gas atmosphere of N 2 :H 2 =9:1, pass into the tubular furnace at a gas flow rate of 100 mL / min, and heat up to 700 °C at a rate of 4 °C / min, and keep the temperature constant and calcine for 4 h. After cooling to room temperature, the Fe / Fe 3 C-MOR core-shell structure catalyst is obtained.

[0063] Use the obtained Fe / Fe 3 C-MOR catalyst to catalyze the depolymerization of lignin: Add 1.0017 g of sulfonated lignin and 0.1976 g of Fe / Fe 3 C-MOR catalyst to 30 mL of absolute ethanol, then put it into a 100 mL batch high-temperature and high-pressure reactor. Under the protection of high-purity nitrogen, stir at a rotation speed of 480 r / min for 30 min, and then at a temperature of 290 °C and a pressure of 7.5 MPa, form a supercritical ethanol system, react for 3 h. After the reaction is completed, lower the temperature of the reactor to 250 °C, place the reactor in an ice-water bath for rapid cooling, and after cooling to 25 °C room temperature, filter by suction, and under the conditions of a temperature of 46 °C and a rotation speed of 75 r / min, vacuum rotary evaporate the obtained filtrate to remove absolute ethanol to obtain a liquid-phase product.

[0064] Perform X-ray diffraction on the Fe / Fe 3 C-MOR catalyst obtained in Example 4, and it can be seen that Fe and Fe 3 C phases are loaded on the surface of the catalyst. At this time, the mordenite structure breaks and forms a crystal SiO 2 structure.

[0065] The Fe / Fe 3The BET analysis of the C-MOR catalyst shows that a large number of microporous structures are formed on the catalyst surface, which has a good adsorption effect on lignin and promotes the catalytic depolymerization of lignin.

[0066] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, the calcination is directly carried out in a reducing gas atmosphere to form the calcined MOR.

[0067] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, the calcination is directly carried out in a reducing gas atmosphere to form Fe / Fe 3 C-C catalyst.

[0068] The liquid-phase products after the depolymerization of lignin by the catalysts of Examples 1-4 were qualitatively and quantitatively analyzed by GC-MS technology. After calculation, the lignin conversion rate and the selectivity of phenolic monomers were obtained, and the results are shown in Table 1:

[0069] Table 1 Catalyst compositions and catalytic efficiency results of Examples 1-4 and Comparative Examples 1-2

[0070]

[0071]

[0072] As can be seen from Table 1, compared with Comparative Examples 1-2, Examples 1-4 significantly improved the conversion rate of lignin and the selectivity of phenolic monomers by the catalyst, indicating that the catalyst prepared by the present invention can catalytically depolymerize lignin to selectively generate phenolic monomers with high selectivity. Comparing Example 1 with Comparative Examples 1-2, it can be seen that Fe / Fe 3 The C catalytic phase and the MOR support have a synergistic catalytic effect on the depolymerization of lignin. The reason may be that Fe / Fe 3 The C-MOR catalyst uses the active metal Fe to promote the generation of more Brønsted acid (B acid) and Lewis acid (L acid) active sites on MOR, and activates hydrogen radicals through the Fe / Fe 3 C metal active sites, and further forms alkyl radicals through the B acid and L acid active sites, synergistically promoting the cleavage of C-C and C-O bonds in lignin. At the same time, under the condition of a reducing atmosphere, a large number of oxygen vacancies are generated on the surface of the Fe / Fe 3 C-MOR catalyst, and the doping of Fe causes the structure of MOR to be damaged, forming a crystal SiO 2 structure, so that its surface is loaded with Fe / Fe 3 C to form a core-shell structure, which also helps to improve the adsorption of lignin molecules by the catalyst and the effective contact between the active catalytic components and lignin. In addition, the increase in the content of EDTA-Fe,Na also improves the conductivity of the catalyst, and the higher electron cloud density on its surface may help to adsorb and activate lignin molecules and promote the electron transfer during the reaction, thereby promoting the cracking reaction and improving the efficiency of lignin depolymerization.

[0073] The inventors also found that the Fe / Fe 3 C-MOR catalyst prepared in Example 3 has the best catalytic effect on lignin depolymerization, with a lignin conversion rate as high as 96.49% and a selectivity for phenolic monomers as high as 78.80%. That is, the mass ratio of EDTA-Fe,Na to MOR of 0.6:0.4 is the optimal ratio of the catalyst of the present invention.

[0074] Meanwhile, for the Fe / Fe 3 C-MOR catalysts prepared in Examples 1-3, with the increase of the content of EDTA-Fe,Na, the lignin conversion rate and the selectivity for phenolic monomers increase. This shows that within a certain range, increasing the content of Fe / Fe 3 C in the catalyst system helps to improve the catalytic depolymerization performance of the catalyst for lignin. Comparing the data of Example 3 and Example 4, it can be seen that when the mass ratio of EDTA-Fe,Na to MOR is higher than 0.6:0.4, the lignin conversion rate and the selectivity for phenolic monomers of the catalyst decrease again. The reason for the analysis is that when the content of the Fe / Fe 3 C catalytic phase in the catalyst system is too high, the content of MOR decreases accordingly, and the number of microporous structures in the catalyst decreases, affecting the adsorption and contact performance of the catalyst for lignin molecules. This may be an important reason for the decrease in the catalytic depolymerization performance of the catalyst for lignin in Example 4.

[0075] Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0076] The present invention aims to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a Fe / Fe3C-MOR core-shell structure catalyst for catalytic depolymerization of lignin, characterized in that: The following steps are involved: (1) Add ethylenediaminetetraacetic acid sodium iron salt into deionized water, stir and dissolve into a yellow-brown transparent solution to obtain EDTA-Fe,Na solution; (2) adding commercial mordenite to EDTA-Fe,Na solution, mixing evenly, heating and stirring in a constant temperature water bath at 60-70°C for 4 h, evaporating deionized water at 80-90°C, drying in an oven at 105°C overnight, grinding, and passing through an 80-mesh sieve to obtain a solid powder; (3) The obtained solid powder is placed in a tubular calcining furnace, heated to 700°C in a reducing gas atmosphere, and calcined at a constant temperature. After cooling to room temperature, a Fe / Fe3C-MOR core-shell structure catalyst is obtained.

2. The method for preparing a Fe / Fe3C-MOR core-shell structure catalyst for catalytic depolymerization of lignin according to claim 1, characterized in that: The usage ratio of ethylenediaminetetraacetic acid sodium iron salt, deionized water and commercial mordenite is 0.2-0.8g:50mL:0.2g-0.8g.

3. The method for preparing a Fe / Fe3C-MOR core-shell structure catalyst for catalytic depolymerization of lignin according to claim 1, characterized in that: Step (3) is specifically as follows: the obtained solid material is loaded into a tubular calcining furnace, and in a reducing gas atmosphere of N2:H2=9:1, an air flow rate of 50-100 mL / min is passed into the tubular furnace, and the temperature is increased to 700°C at a rate of 4°C / min, and calcined at a constant temperature for 4 hours, and then cooled to room temperature.

4. An application of the Fe / Fe3C-MOR core-shell structure catalyst obtained by the preparation method according to any one of claims 1 to 3 in catalytic depolymerization of lignin to generate phenol monomer compounds with high selectivity.

5. The use according to claim 4, characterized in that: The application method is as follows: adding raw material lignin and Fe / Fe3C-MOR catalyst into anhydrous ethanol, placing the mixture into an intermittent high-temperature and high-pressure reactor, stirring at a speed of 400-500 r / min for 20-50 min under an inert gas, and keeping the reaction temperature for 3-4 h at a temperature of 270°C-310°C and a pressure of 6.5-8.5 MPa. After the reaction is completed, lowering the temperature of the reactor to below 250°C, and then placing the reactor in an ice-water bath for quenching. After cooling to room temperature, filtering and vacuum rotary evaporation are performed to obtain lignin oil.

6. The use according to claim 5, characterized in that: The inert gas is high-purity argon or high-purity nitrogen.

7. The use according to claim 5, characterized in that: The usage ratio of the lignin, Fe / Fe3C-MOR catalyst and anhydrous ethanol is 0.99-1.01g:0.19-0.21g: 30mL.

8. The use according to claim 5, characterized in that: The temperature of the vacuum rotary evaporation is 40-47° C. and the rotation speed is 65-95 r / min.

9. The use according to claim 5 or 7, characterized in that: The raw material lignin is one or more of original lignin, alkali lignin and sulfonate lignin.

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