Ni-CeO2 / MMO catalyst, preparation and application thereof

Abstract

The application discloses a Ni-CeO2 / MMO catalyst and a preparation and application thereof. The preparation method comprises the following steps: dissolving Ni(NO3)2.6H2O, Mg(NO3)2.6H2O and metal nitrate A in a solvent, performing a hydrothermal crystallization reaction after adjusting the pH of the solution; lowering to room temperature after the reaction is finished, and then separating, washing, drying and grinding into powder to obtain an LDHs precursor; immersing the LDHs precursor in a Ce(NO3)3 aqueous solution and stirring, and then filtering, drying, calcining in an air atmosphere and reducing in a H2 / N2 mixed gas to obtain the Ni-CeO2 / MMO catalyst. The Ni-CeO2 / MMO catalyst integrates depolymerization, hydrogenation and carbon deposition reduction, and has the advantages of simple preparation process and low cost. When the catalyst prepared by the application is applied to a lignin hydrogenolysis reaction process, a higher lignin conversion rate can be obtained, the yield of liquid phase products reaches more than 80%, and the selectivity of monomer phenol in the products is greater than 40%.

Description

Technical Field

[0001] This invention relates to the field of biomass conversion technology, specifically to a Ni-CeO2 / MMO catalyst and its preparation and application. Background Technology

[0002] Biomass mainly includes cellulose, hemicellulose and lignin. Among them, lignin is difficult to be widely used due to its very stable structure. Aromatic compounds obtained by degrading lignin through chemical methods can be used as raw materials for the production of high-value-added chemicals such as pharmaceuticals, resins and dyes.

[0003] Hydrogenolysis is an important method for achieving lignin depolymerization. Commonly used catalysts include homogeneous and heterogeneous catalysts. Heterogeneous catalysts are widely used due to their advantages such as easy separation and recyclability. Commonly used heterogeneous catalysts include noble metal (Pt, Pd, Ru, Rh, etc.) catalysts, transition metal (Ni, Mo, Co, W, etc.) catalysts, bimetallic catalysts, sulfide catalysts, nitride catalysts, and phosphide catalysts. Ni-based catalysts have advantages such as good catalytic effect and low cost, and are often used to catalyze the hydrogenolysis of lignin. Cui Qingyan (CN114588910B) used activated carbon-supported Ni-Zn to catalyze the hydrogenolysis of gramineous lignin in a suspension bed. When the catalyst / lignin ratio was 40%, the liquid phase product yield reached over 65%, and the selectivity of phenolic compounds was greater than 36 wt.%. Shen Dekui (CN114213222A) used NiCu / C to catalyze the hydrogenolysis of poplar lignin in an organic solvent, achieving a phenolic monomer yield of over 50 wt.%.

[0004] During catalytic hydrogenolysis, carbon deposits inevitably form on the catalyst surface. As the catalytic reaction proceeds, the number of active sites in contact with lignin decreases, leading to a continuous decline in catalytic activity. Therefore, introducing components that inhibit carbon deposition to improve catalyst activity is of great significance for the hydrogenolysis of lignin.

[0005] CN118459321A discloses a method for selectively hydrogenating lignin to obtain C6 monophenols, comprising: using the hydrogen-containing functional groups of lignin itself as the hydrogen source for reductive depolymerization in an aqueous solvent system, and selectively converting lignin to C6 monophenols in a one-pot process. Specifically, this technology uses hydroxyapatite as a support, loaded with a certain amount of metal. Lignin, catalyst, and water are placed together in a reactor, purged and sealed with nitrogen gas, and subjected to hydrogenolysis at a specific temperature and time. After the reaction, the mixture is extracted with ethyl acetate in three portions to remove the lignin monomers, ultimately yielding C6 monophenols (phenol, guaiacol, and 2,6-dimethoxyphenol) with a selectivity as high as 74.4%. The catalysts used include one or more combinations of hydroxyapatite, silica, hydrotalcite, magnesium oxide, metal oxides, and metal nitride supports. Although the catalyst used in this technology can achieve high selectivity for C6 monophenols in the hydrogenolysis reaction, it is prepared by a one-pot method. The disordered assembly of the support material limits the subsequent loading of active metal elements on the catalyst. Furthermore, during the catalytic reaction, the catalyst can only exert its catalytic effect on the active sites on the outer surface of the catalyst, which further limits the catalytic efficiency of the catalyst.

[0006] CN115041190A discloses the preparation and application of a highly dispersed Ni-Ru / Al2O3 catalyst with topological transformation in hydrotalcite. This catalyst uses NiAl hydrotalcite as a precursor, introduces Ru exogenously, and prepares a highly dispersed Ni-Ru / Al2O3 catalyst through topological transformation and in-situ reduction. This catalyst exhibits excellent catalytic performance in the hydrogenolysis of lignin and its model compounds, selectively and actively breaking aryl ether bonds in lignin and its model compounds under mild conditions, significantly outperforming commercial Ru / C catalysts. While the catalyst achieves excellent reaction performance in hydrogenolysis, its preparation process using a one-step method for the Ni-Al hydrotalcite support is problematic. During this process, Ni agglomeration easily occurs, making it difficult to maintain high Ni dispersion in the support. Furthermore, whether the synergistic effect between Ni and Ru can be fully utilized in the subsequent Ru loading process requires further investigation.

[0007] CN113231075A discloses a method for depolymerizing lignin into cyclohexanol compounds using RuNi supported on hydrotalcite oxide. This technique combines the lamellar structure and weak basicity of DMO, using Ru and Ni as active centers for lignin hydrogenolysis. The Ru / DMO method exhibits extremely high activity in lignin hydrogenation systems, achieving a cyclohexanol yield of 8.47 wt% under conditions of 280℃, 4 MPa H2, 40 mL water, and 8 hours. Furthermore, the yield did not significantly decrease after three catalyst reuses. However, the disclosed DMO preparation scheme employs traditional co-precipitation for support preparation. The assembly of the support material in this process is affected by various preparation conditions, making it difficult to guarantee the repeatability of the structural properties of the resulting support.

[0008] CN112341312A discloses a method for selective hydrogenolysis of lignin to prepare cyclohexanol and its derivatives. This method involves mixing ruthenium-supported hydrotalcite oxide, lignin, and a solvent, reacting the mixture at 200–280°C and H2 pressure of 1–5 MPa for 2–10 hours, followed by solid-liquid separation to obtain a product mixture containing cyclohexanol and its derivatives. The preparation process of the hydrotalcite oxide involves uniformly mixing Mg(NO3)2·6H2O and Al(NO3)3·9H2O with water, then adding the mixture to a Na2CO3 solution at a certain rate, while simultaneously adjusting the pH of the system to 10 using NaOH solution. The mixture is then subjected to aging, washing, and calcination steps. Although the catalyst used in this technology achieves high product selectivity during the hydrogenolysis reaction, the catalyst support is prepared by chemical precipitation. The disordered assembly of the support material limits the subsequent loading of active metal elements into the prepared catalyst. Furthermore, during the catalytic reaction, the catalyst can only exert its catalytic effect at the active sites on its outer surface, further limiting the catalytic efficiency. Summary of the Invention

[0009] The purpose of this invention is to provide a Ni-CeO2 / MMO catalyst and its preparation and application. This invention utilizes an impregnation method to support Ce on a hydrotalcite-based solid alkali oxide, and then reduces it to obtain elemental Ni, thus preparing a multifunctional catalyst integrating depolymerization, hydrogenation, and carbon deposition reduction. The preparation process is simple and inexpensive. Applying the catalyst prepared by this invention to the lignin hydrogenolysis reaction yields a higher lignin conversion rate, with a liquid-phase product yield exceeding 80% and a phenol selectivity of over 40% in the product.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] The first aspect of this invention provides a method for preparing a Ni-CeO2 / MMO catalyst, wherein the preparation method includes the following steps:

[0012] Ni(NO3)2·6H2O, Mg(NO3)2·6H2O, and metal nitrate A are dissolved in a solvent, wherein metal nitrate A is selected from at least one of Fe(NO3)3·9H2O, Al(NO3)3·9H2O, and Co(NO3)3·6H2O; the pH of the solution is adjusted to 8-12 and then a hydrothermal crystallization reaction is carried out; after the reaction is completed, the temperature is lowered to room temperature, the solid is separated, washed, dried, and ground into powder to obtain the LDHs precursor;

[0013] The LDH precursor was impregnated in an aqueous Ce(NO3)3 solution and stirred. After filtration, drying, and grinding into powder, the powder was calcined in an air atmosphere and then reduced in a H2 / N2 mixed gas to obtain the Ni-CeO2 / MMO catalyst.

[0014] In the preparation method of this invention, the first step is mainly a hydrolysis reaction. By controlling the pH value of the synthesis system, the hydrolysis rate of each metal element is adjusted to prepare LDHs precursors. Then, Ce is loaded onto the substrate. During the air calcination process, both Ce and Ni elements are oxidized. In the subsequent reduction process, since Ce is more difficult to be reduced by hydrogen than Ni, Ni elements in the composite oxide crystal are reduced to elemental Ni. The elemental Ni then detaches from the crystal and combines with the oxygen storage component CeO2 on the surface, together serving as catalytic active sites to exert multifunctional catalytic effects such as depolymerization, hydrogenation, and reduction of carbon deposition.

[0015] According to the preparation method of the present invention, preferably, the molar ratio of Ni(NO3)2·6H2O, Mg(NO3)2·6H2O and metal nitrate A is 1:(1~5):(1~1.5).

[0016] According to the preparation method of the present invention, preferably, the solvent is an ethanol-water mixed solvent. More preferably, the volume ratio of ethanol in the ethanol-water mixed solvent is (5-30) vol.%. Even more preferably, the molar ratio of metal nitrate to water in the reaction system is 1:(30-45), wherein the metal nitrate includes Ni(NO3)2·6H2O, Mg(NO3)2·6H2O, and metal nitrate A.

[0017] According to the preparation method of the present invention, preferably, the pH value of the solution is adjusted using NaOH solution. The specific concentration of the NaOH solution can be, for example, 2 mol / L, etc., but the present invention does not limit this.

[0018] According to the preparation method of the present invention, preferably, the temperature of the hydrothermal crystallization reaction is 160-300°C and the time is 12-24h.

[0019] According to the preparation method of the present invention, preferably, the concentration of the Ce(NO3)3 aqueous solution is 0.1-1 mol / L, and n(Ni 2+ ):n(Ce 3+ =1:(2.5~12).

[0020] According to the preparation method of the present invention, preferably, the LDHs precursor is immersed in Ce(NO3)3 solution and stirred for 1 to 3 hours.

[0021] According to the preparation method of the present invention, preferably, the calcination temperature in the air atmosphere is 600-900°C and the time is 8-12 hours.

[0022] According to the preparation method of the present invention, preferably, in the H2 / N2 mixed gas, the volume ratio of H2 to N2 is 1:(4-10), the flow rate of the H2 / N2 mixed gas is 50-150 mL / min, the reduction temperature is 400-700℃, and the reduction time is 2-5 h.

[0023] A second aspect of the present invention provides a Ni-CeO2 / MMO catalyst, which is obtained by any of the above preparation methods.

[0024] A third aspect of the present invention provides a method for applying the above-described Ni-CeO2 / MMO catalyst in the catalytic hydrogenolysis of lignin, comprising the following steps:

[0025] Lignin and the Ni-CeO2 / MMO catalyst were added to a hydrogen-donating solvent and depolymerized at 200–350 °C. After the reaction was completed, the mixture was cooled to room temperature and filtered. The hydrogen-donating solvent was removed from the liquid phase. Then, hydrochloric acid solution was added for acidification, followed by extraction with ethyl acetate. The upper liquid was dried and the ethyl acetate was removed to obtain the liquid product.

[0026] Preferably, the lignin is an organic solvent lignin or lignin sulfonate.

[0027] Preferably, the mass ratio of lignin to Ru-Ni / NiO-MMO catalyst is (2-4):1.

[0028] Preferably, the hydrogen-donating solvent is selected from at least one of ethanol, isopropanol, n-butanol, sec-butanol, and tert-butanol.

[0029] Preferably, the depolymerization reaction takes 2 to 12 hours.

[0030] Preferably, the acidification is carried out to pH=1.

[0031] The beneficial effects of this invention include:

[0032] (1) In this invention, Ce is loaded onto a hydrotalcite-based solid alkali oxide by an impregnation method, and Ni is obtained by reduction. 0 A multifunctional catalyst integrating depolymerization, hydrogenation, and carbon deposition reduction was prepared, and the preparation process is simple and inexpensive.

[0033] (2) This invention utilizes Ru-Ni / NiO-MMO to catalyze the hydrogenolysis of lignin, with a liquid phase product yield of over 80%. The liquid phase product contains phenols, guaiacols, syringols and their corresponding derivatives, with a selectivity of over 40% for phenols and their corresponding derivatives. Attached Figure Description

[0034] Figure 1 The catalyst Ni-CeO2 / MgFeO prepared in Example 1 x SEM image. Detailed Implementation

[0035] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0036] All numerical specifications in this invention (e.g., temperature, time, concentration, and weight, including ranges for each) are generally approximate values ​​that may be changed (+) or (-) in increments of 0.1 or 1.0. All numerical specifications are to be understood as being preceded by the term "about".

[0037] Example 1:

[0038] This embodiment prepares a Ni-CeO2 / MgFeO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0039] Weigh 1.163g Ni(NO3)2·6H2O, 3.077g Mg(NO3)2·6H2O, and 1.616g Fe(NO3)3·9H2O and add them to a polytetrafluoroethylene reactor. Add 50mL of ethanol-water solution (ethanol content 10 vol.%) to completely dissolve the metal nitrates. Adjust the pH of the solution to 9 with 2mol / L NaOH solution, and then perform hydrothermal crystallization at 200℃ for 24h. After crystallization, cool to room temperature, wash with deionized water, and centrifuge until the supernatant is neutral. Dry the obtained product in a vacuum drying oven and grind it into powder.

[0040] The obtained LDH precursor was impregnated in 20 mL of 0.5 mol / L Ce(NO3)3 solution, stirred for 2 h, and then filtered. The filter cake was dried and ground in a vacuum drying oven, and the powder was calcined in a tube furnace under air atmosphere at a temperature of 900 °C for 8 h. The resulting powder was then reduced in a H2 / N2 mixture at a temperature of 550 °C for 5 h, with a flow rate of 50 mL / min and a volume ratio of H2 to N2 of 1:10, to obtain Ni-CeO2 / MgFeO. x Its SEM image is as follows: Figure 1 As shown, from Figure 1 It can be seen that the prepared Ni-CeO2 / MgFeO x The catalyst has a layered structure.

[0041] 1g of organic solvent lignin and 0.5g of Ni-CeO2 / MgFeO x The product was added to 50 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 0.813 g of liquid product, which represents a liquid phase product yield of 81.3%. The main products were cyclohexanol, phenol, guaiacol, eugenol, and their corresponding derivatives, with a selectivity of 42.7% for phenol and its derivatives.

[0042] Example 2:

[0043] This embodiment prepares a Ni-CeO2 / MgCoO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0044] Weigh 1.454 g Ni(NO3)2·6H2O, 3.846 g Mg(NO3)2·6H2O, and 1.455 g Co(NO3)2·6H2O and add them to a polytetrafluoroethylene reactor. Add 50 mL of ethanol-water solution (ethanol content 15 vol.%) to dissolve the metal nitrate. Adjust the pH of the solution to 10 with 2 mol / L NaOH solution, and then perform hydrothermal crystallization at 160℃ for 24 h. After crystallization, cool to room temperature, wash with deionized water, and centrifuge until the supernatant is neutral. Dry the obtained product in a vacuum drying oven and grind it into powder. The obtained LDH precursor was impregnated in 25 mL of 0.5 mol / L Ce(NO3)3 solution and stirred for 3 h. After filtration, the filter cake was dried and ground in a vacuum drying oven. The powder was then calcined in a tube furnace under an air atmosphere at 900 °C for 8 h. The resulting powder was then reduced in a H2 / N2 mixture at 600 °C for 5 h with a flow rate of 50 mL / min and a volume ratio of H2 to N2 of 1:10, yielding Ni-CeO2 / MgCoO2. x .

[0045] 2g of organic solvent lignin and 0.5g of Ni-CeO2 / MgCoO x The product was added to 60 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 1.638 g of liquid product, i.e., the liquid phase product yield reached 81.9%, and the selectivity of phenol and its derivatives in the liquid phase product was 44.3%.

[0046] Example 3:

[0047] This embodiment prepares a Ni-CeO2 / MgAlO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0048] 1.454 g Ni(NO3)2·6H2O, 3.846 g Mg(NO3)2·6H2O, and 1.876 g Al(NO3)3·9H2O were weighed and added to a polytetrafluoroethylene reactor. 50 mL of an ethanol-water solution (15 vol.%) was added to neutralize the metal nitrate. The pH of the solution was adjusted to 10 with 2 mol / L NaOH solution, and then hydrothermally crystallized at 180 °C for 24 h. After crystallization, the solution was cooled to room temperature, washed with deionized water, and centrifuged until the supernatant was neutral. The resulting product was dried in a vacuum drying oven and then ground into powder. The obtained LDH precursor was impregnated in 25 mL of 0.5 mol / L Ce(NO3)3 solution and stirred for 3 h. After filtration, the filter cake was dried and ground in a vacuum drying oven. The powder was then calcined in a tube furnace under an air atmosphere at a temperature of 900 °C for 8 h. The resulting powder was then reduced in a H2 / N2 mixture at a temperature of 600 °C for 5 h. The H2 / N2 mixture flow rate was 50 mL / min, and the volume ratio of H2 to N2 was 1:10, yielding Ni-CeO2 / MgAlO2. x .

[0049] 1g of organic solvent lignin was mixed with 0.5g of Ni-CeO2 / MgAlO x The product was added to 60 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 0.823 g of liquid product, i.e., the liquid phase product yield reached 82.3%, and the selectivity of phenol and its derivatives in the liquid phase product was 41.5%.

[0050] Example 4:

[0051] This embodiment prepares a Ni-CeO2 / MgFeO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0052] Ni-CeO2 / MgFeO x The preparation process is the same as in Example 1.

[0053] 2g of calcium lignosulfonate and 0.5g of Ni-CeO2 / MgFeO xThe product was added to 60 mL of anhydrous ethanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 300 °C for 3 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 1.658 g of liquid product, i.e., the liquid phase product yield reached 82.9%, and the selectivity of phenol and its derivatives in the liquid phase product was 44.3%.

[0054] Example 5

[0055] This embodiment prepares a Ni-CeO2 / MgFeO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0056] Weigh 1.163g Ni(NO3)2·6H2O, 5.128g Mg(NO3)2·6H2O, and 2.424g Fe(NO3)3·9H2O and add them to a polytetrafluoroethylene reactor. Add 50mL of ethanol-water solution (ethanol content 10 vol.%) to completely dissolve the metal nitrates. Adjust the pH of the solution to 9 with 2mol / L NaOH solution, and then perform hydrothermal crystallization at 300℃ for 12h. After crystallization, cool to room temperature, wash with deionized water, and centrifuge until the supernatant is neutral. Dry the obtained product in a vacuum drying oven and grind it into powder.

[0057] The obtained LDH precursor was impregnated in 20 mL of 0.5 mol / L Ce(NO3)3 solution, stirred for 1 h, and then filtered. The filter cake was dried and ground in a vacuum drying oven, and the powder was calcined in a tube furnace under air atmosphere at a temperature of 600 °C for 12 h. The resulting powder was then reduced in a H2 / N2 mixture at a temperature of 400 °C for 5 h, with a flow rate of 50 mL / min and a volume ratio of H2 to N2 of 1:10, to obtain Ni-CeO2 / MgFeO. x .

[0058] 1g of organic solvent lignin and 0.5g of Ni-CeO2 / MgFeO xThe product was added to 50 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 0.769 g of liquid product, i.e., the liquid phase product yield reached 76.9%. The main products were cyclohexanol, phenol, guaiacol, eugenol, and their corresponding derivatives, with a selectivity of 41.0% for phenol and its derivatives.

[0059] Example 6:

[0060] This embodiment prepares a Ni-CeO2 / MgCoO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0061] Weigh 1.454 g Ni(NO3)2·6H2O, 5.128 g Mg(NO3)2·6H2O, and 1.455 g Co(NO3)2·6H2O and add them to a polytetrafluoroethylene reactor. Add 50 mL of ethanol-water solution (ethanol content 15 vol.%) to dissolve the metal nitrate. Adjust the pH of the solution to 10 with 2 mol / L NaOH solution, and then perform hydrothermal crystallization at 300℃ for 12 h. After crystallization, cool to room temperature, wash with deionized water, and centrifuge until the supernatant is neutral. Dry the obtained product in a vacuum drying oven and grind it into powder. The obtained LDH precursor was impregnated in 25 mL of 0.5 mol / L Ce(NO3)3 solution and stirred for 3 h. After filtration, the filter cake was dried and ground in a vacuum drying oven. The powder was then calcined in a tube furnace under an air atmosphere at 600 °C for 12 h. The resulting powder was reduced in a H2 / N2 mixture at 700 °C for 2 h with a flow rate of 150 mL / min and a volume ratio of H2 to N2 of 1:10, yielding Ni-CeO2 / MgCoO2. x .

[0062] 2g of organic solvent lignin and 0.5g of Ni-CeO2 / MgCoO xThe product was added to 60 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 1.564 g of liquid product, i.e., the liquid phase product yield reached 78.2%, and the selectivity of phenol and its derivatives in the liquid phase product was 42.9%.

[0063] Example 7

[0064] This embodiment prepares a Ni-CeO2 / MgFeO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0065] Weigh 1.163g Ni(NO3)2·6H2O, 3.077g Mg(NO3)2·6H2O, and 1.616g Fe(NO3)3·9H2O and add them to a polytetrafluoroethylene reactor. Add 50mL of ethanol-water solution (ethanol content 10 vol.%) to completely dissolve the metal nitrates. Adjust the pH of the solution to 9 with 2mol / L NaOH solution, and then perform hydrothermal crystallization at 200℃ for 24h. After crystallization, cool to room temperature, wash with deionized water, and centrifuge until the supernatant is neutral. Dry the obtained product in a vacuum drying oven and grind it into powder.

[0066] The obtained LDH precursor was impregnated in 20 mL of 0.5 mol / L Ce(NO3)3 solution, stirred for 1 h, and then filtered. The filter cake was dried and ground in a vacuum drying oven, and the powder was calcined in a tube furnace under air atmosphere at a temperature of 600 °C for 12 h. The resulting powder was then reduced in a H2 / N2 mixed gas at a reduction temperature of 400 °C for 3 h, with a flow rate of 50 mL / min and a volume ratio of H2 to N2 of 1:4, to obtain Ni-CeO2 / MgFeO. x .

[0067] 1g of organic solvent lignin and 0.5g of Ni-CeO2 / MgFeO xThe product was added to 50 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 0.808 g of liquid product, i.e., the liquid phase product yield reached 80.8%. The main products were cyclohexanol, phenol, guaiacol, syringol, and their corresponding derivatives, with a selectivity of 45.4% for phenol and its derivatives.

[0068] Example 8

[0069] This embodiment prepares a Ni-CeO2 / MgAlO x The catalyst, and its use in the catalytic hydrogenolysis of lignin, includes the following steps:

[0070] 1.454 g Ni(NO3)2·6H2O, 5.128 g Mg(NO3)2·6H2O, and 1.876 g Al(NO3)3·9H2O were weighed and added to a polytetrafluoroethylene reactor. 50 mL of an ethanol-water solution (15 vol.%) was added to neutralize the metal nitrate. The pH of the solution was adjusted to 10 with 2 mol / L NaOH solution, and then hydrothermally crystallized at 200 °C for 24 h. After crystallization, the solution was cooled to room temperature, washed with deionized water, and centrifuged until the supernatant was neutral. The resulting product was dried in a vacuum drying oven and then ground into powder. The obtained LDH precursor was impregnated in 25 mL of 0.5 mol / L Ce(NO3)3 solution and stirred for 3 h. After filtration, the filter cake was dried and ground in a vacuum drying oven. The powder was then calcined in a tube furnace under air atmosphere at a temperature of 900 °C for 12 h. The resulting powder was reduced in a H2 / N2 mixed gas at a temperature of 500 °C for 5 h. The H2 / N2 mixed gas flow rate was 150 mL / min, and the volume ratio of H2 to N2 was 1:4, yielding Ni-CeO2 / MgAlO2. x .

[0071] 1g of organic solvent lignin was mixed with 0.5g of Ni-CeO2 / MgAlO xThe product was added to 60 mL of isopropanol, purged with N2 for 20 min, and then subjected to a depolymerization reaction in a high-temperature, high-pressure reactor at 270 °C for 4 h. After the reaction, the mixture was cooled to room temperature, filtered to separate the liquid and solid phases, and the isopropanol was removed from the liquid phase using a rotary evaporator. Then, 1 mol / L hydrochloric acid was added to adjust the pH to 1, and the mixture was extracted three times with ethyl acetate. The supernatant was dried with anhydrous MgSO4, and then the ethyl acetate was removed by rotary evaporation to obtain 0.811 g of liquid product, i.e., the liquid phase product yield reached 81.1%, and the selectivity of phenol and its derivatives in the liquid phase product was 40.3%.

[0072] Comparative Example 1:

[0073] The organic solvent lignin was depolymerized according to the method of Example 1, except that the catalyst preparation process did not involve reduction by H2 / N2 mixed gas, and the yield of liquid phase product was 67.3%, of which the selectivity for phenol and its derivatives was 35.5%.

[0074] Comparative Example 2:

[0075] The organic solvent lignin was depolymerized according to the method of Example 1, except that Ce was not loaded on the catalyst. The yield of the liquid phase product after the catalytic reaction was 72.3%, of which the selectivity for phenol and its derivatives was 41.2%.

[0076] Comparative Example 3:

[0077] The method of Example 4 was used to depolymerize calcium lignosulfonate, except that no Ni was used in the catalyst preparation process. The yield of the liquid phase product after the catalytic reaction was 52.7%, of which the selectivity for phenol and its derivatives was 36.4%.

[0078] The depolymerization results of lignin in the above examples and comparative examples are summarized in Table 1. As can be seen from Comparative Examples 1 and 3, Ni, as the catalytically active element in the lignin depolymerization reaction, primarily exhibits elemental Ni. When Ni is loaded onto the catalyst surface using only a loading and calcination process, it mainly exists as an oxide on the catalyst surface, which cannot serve as an effective catalytic active site for lignin depolymerization. Comparing the reaction results of Comparative Example 2 with those of Example 1 shows that the introduction of CeO2 is beneficial for improving catalyst activity. This is partly due to the co-catalytic effect of CeO2 on the catalytic active sites, and partly because the lattice oxygen in CeO2 catalyzes the oxidation of the depolymerization reaction to generate coke, thus avoiding the problem of reduced catalyst activity caused by coke covering the Ni catalytic active sites.

[0079] Table 1. Statistical Table of Evaluation Results of Lignin Depolymerization Reaction

[0080] Project Name Liquid phase yield / wt% Monomer phenol selectivity / % Example 1 81.3 42.7 Example 2 81.9 44.3 Example 3 82.3 41.5 Example 4 82.9 44.3 Example 5 76.9 41.0 Example 6 78.2 42.9 Example 7 80.8 45.4 Example 8 81.1 40.3 Comparative Example 1 67.3 35.5 Comparative Example 2 72.3 41.2 Comparative Example 3 52.7 36.4

[0081] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a Ni-CeO2 / MMO catalyst, wherein, The preparation method includes the following steps: Ni(NO3)2·6H2O, Mg(NO3)2·6H2O, and metal nitrate A are dissolved in a solvent, wherein metal nitrate A is selected from at least one of Fe(NO3)3·9H2O, Al(NO3)3·9H2O, and Co(NO3)3·6H2O; the pH of the solution is adjusted to 8-12 and then a hydrothermal crystallization reaction is carried out; after the reaction is completed, the temperature is lowered to room temperature, the solid is separated, washed, dried, and ground into powder to obtain the LDHs precursor; The LDH precursor was impregnated in an aqueous Ce(NO3)3 solution and stirred. After filtration, drying, and grinding into powder, the powder was calcined in an air atmosphere and then reduced in a H2 / N2 mixed gas to obtain the Ni-CeO2 / MMO catalyst.

2. The preparation method according to claim 1, wherein, The molar ratio of Ni(NO3)2·6H2O, Mg(NO3)2·6H2O and metal nitrate A is 1:(1~5):(1~1.5).

3. The preparation method according to claim 1, wherein, The solvent is an ethanol-water mixture.

4. The preparation method according to claim 1, wherein, The hydrothermal crystallization reaction is carried out at a temperature of 160–300°C for 12–24 hours.

5. The preparation method according to claim 1, wherein, The concentration of the Ce(NO3)3 aqueous solution is 0.1–1 mol / L, n(Ni 2+ ):n(Ce 3+ =1:(2.5~12).

6. The preparation method according to claim 1, wherein, The LDH precursor was immersed in Ce(NO3)3 solution and stirred for 1-3 hours.

7. The preparation method according to claim 1, wherein, The calcination temperature in the air atmosphere is 600–900℃, and the time is 8–12 hours.

8. The preparation method according to claim 1, wherein, In the H2 / N2 mixture, the volume ratio of H2 to N2 is 1:(4~10), the flow rate of the H2 / N2 mixture is 50~150mL / min, the reduction temperature is 400~700℃, and the reduction time is 2~5h.

9. A Ni-CeO2 / MMO catalyst, obtained by the preparation method according to any one of claims 1-8.

10. A method for using the Ni-CeO2 / MMO catalyst of claim 9 in the catalytic hydrogenolysis of lignin, wherein, The application method includes the following steps: Lignin and the Ni-CeO2 / MMO catalyst were added to a hydrogen-donating solvent and depolymerized at 200–350 °C. After the reaction was completed, the mixture was cooled to room temperature and filtered. The hydrogen-donating solvent was removed from the liquid phase. Then, hydrochloric acid solution was added for acidification, followed by extraction with ethyl acetate. The upper liquid was dried and the ethyl acetate was removed to obtain the liquid product.

11. The application method according to claim 10, wherein, The mass ratio of lignin to Ru-Ni / NiO-MMO catalyst is (2-4):

1.

12. The application method according to claim 10, wherein, The hydrogen-donating solvent is selected from at least one of ethanol, isopropanol, n-butanol, sec-butanol, and tert-butanol.

13. The application method according to claim 10, wherein, The depolymerization reaction takes 2 to 12 hours.

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