Method for preparing strongly acidic Al-MCM-41 mesoporous catalyst and application of strongly acidic Al-MCM-41 mesoporous catalyst

Abstract

The invention belongs to the field of inorganic non-metallic materials, and particularly relates to a method for preparing a strongly acidic Al-MCM-41-T mesoporous catalyst from an MWW layered molecular sieve precursor through a crystal transformation method and application of the strongly acidic Al-MCM-41-T mesoporous catalyst. Specifically, an aluminum-containing MWW layered molecular sieve precursor (namely MCM-22 (P)) is used as a raw material, and the Al-MCM-41-T catalyst which is large in surface area, high in framework aluminum content and strong in acidity is prepared through a crystal transformation method. The obtained mesoporous material is used for the liquid phase alkylation reaction process of lignin-derived phenols and cyclic alcohols / cycloolefins. The Al-MCM-41-T synthesized by the method has a high specific surface area (more than 1000m < 2 > g <-1 >), a high pore volume (more than 1.4 cm < 3 > g <-1 >) and a regular and concentrated mesoporous structure (2-4nm), meanwhile, the content of framework aluminum is high, and the total Bronsted acid concentration, especially the strong Bronsted acid concentration, is high and far exceeds that of an Al-MCM-41-C material prepared by a conventional hydrothermal method. The catalyst shows excellent activity and polyalkyl product selectivity in an acid-catalyzed liquid-phase alkylation reaction.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic non-metallic materials, and specifically relates to a method and application for preparing a strongly acidic Al-MCM-41-T mesoporous catalyst by a topotactic transformation method using an MWW layered molecular sieve precursor. Background Art

[0002] Aluminum-containing mesoporous Al-MCM-41 molecular sieve materials have large pore sizes, specific surface areas, and adsorption capacities, and show advantages that microporous molecular sieves do not have in processes such as catalysis, adsorption, and separation involving macromolecular reaction substrates or products. Therefore, they have broad application prospects in adsorption and catalysis, especially in the processing of heavy oil and reactions involving biomass-based macromolecules. However, Al-MCM-41 materials prepared by conventional hydrothermal methods usually have a low acid concentration and weak acid strength, and at the same time have poor hydrothermal stability, making it difficult to meet the catalytic processes that require strong acids and harsh conditions, thus restricting the wide application of solid acidic Al-MCM-41 materials. Moreover, the physicochemical properties of Al-MCM-41 largely depend on the preparation conditions, and the factors affecting the growth of mesoporous molecular sieve materials are complex. How to effectively introduce aluminum elements into the mesoporous framework and ensure its structural stability faces challenges.

[0003] Currently reported methods for improving the acidity of Al-MCM-41 mainly include aluminum grafting, post-synthesis, and self-assembly of molecular sieve seeds / precursor solutions, etc. Among them, the molecular sieve seeds / precursor solutions are prepared by self-assembly of molecular sieves including BEA, MFI, and Y seeds or silica-alumina precursor sols and surfactants to prepare mesoporous molecular sieves with strong acidity and high hydrothermal stability [CN1160249C; J. Am. Chem. Soc. 2000, 122, 36, 8791 - 8792; J. Am. Chem. Soc. 2003, 125, 9, 2376 - 2377; J. Am. Chem. Soc. 2001, 123, 21, 5014 - 5021]. These methods of self-assembly using primary or secondary structural units of molecular sieves and surfactant micelles are very effective, and by introducing primary or secondary structural units of zeolites on the pore walls of mesoporous molecular sieves, the acidity of the materials is enhanced. However, the framework silicon and aluminum in the molecular sieve precursors used in the above studies cannot be fully reflected in the finally obtained mesoporous materials, and there is still a lack of effective preparation strategies for the preparation of low-silicon / aluminum ratio Al-MCM-41 in particular.

[0004] In addition, considering the problems of synthesis cost and process operation, there are studies on synthesizing Al-MCM-41 mesoporous molecular sieves by acidifying or alkalizing kaolin, ore mud, attapulgite and fly ash, or even extracting silicon and aluminum sources through high temperature roasting [CN106745032 B; CN 1654330A; CN 104310424 B; CN 106145132B; CN 108928834B], which not only easily causes complex process and low repeatability, but also does not fundamentally solve the problem of low acid concentration and weak acidity of Al-MCM-41. In summary, although the catalyst synthesis method disclosed in the above patent document is helpful to improve the aluminum content and acidity of Al-MCM-41 materials, from the perspective of catalytic application, especially the catalytic reaction process involving strong acid sites (such as carbon-carbon alkylation), the prepared Al-MCM-41 is still difficult to meet the performance requirements. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a method and application of preparing a strongly acidic Al-MCM-41-T mesoporous catalyst by a crystallization method using a MWW layered molecular sieve precursor.

[0006] To achieve the above purpose, the present invention adopts the following technical solution:

[0007] A method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst, using an aluminum-containing MWW layered molecular sieve precursor (i.e., MCM-22(P)) as a raw material, and preparing an Al-MCM-41-T catalyst with a large surface area, a high skeleton aluminum content and strong acidity through a crystal rotation method.

[0008] Further,

[0009] (1) Preparation of MWW layered precursors;

[0010] (2) dispersing the layered precursor in an alkaline solution containing a surfactant and stirring the solution evenly;

[0011] (3) placing the above-obtained solution in a hydrothermal reactor for crystallization treatment;

[0012] (4) The crystallized sample is washed, dried, calcined, and subjected to ammonium ion exchange and secondary calcination to obtain a strongly acidic Al-MCM-41-T material.

[0013] The preparation of the MWW layered molecular sieve precursor is as follows: a silicon source, an aluminum source, a template and an alkali source are dissolved in water and stirred evenly, then transferred to a crystallization kettle for crystallization treatment, and then washed and dried to obtain an MCM-22 (P) precursor; wherein the silicon / aluminum atomic ratio in the precursor feed system is 15-50.

[0014] In the preparation of the MCM-22(P) precursor, the molar ratio of the silicon source, aluminum source, template agent, base source and water is 1.0: 0.008 - 0.035: 0.3 - 0.8: 0.05 - 0.3: 30 - 80, and the crystallization treatment conditions are 140 - 170 °C, rotation speed: 15 - 60 rpm.

[0015] In the preparation of the MCM-22(P) precursor, the silicon source is silica sol, fumed silica, tetraethyl orthosilicate (TEOS); the aluminum source is sodium aluminate (NaAlO2), aluminum sulfate (Al2(SO4)3), aluminum isopropoxide (C9H 21 AlO3).

[0016] The template agent is hexamethyleneimine (HMI), N,N,N-trimethyl-1-adamantyl ammonium hydroxide; the base source is sodium hydroxide (NaOH), potassium hydroxide (KOH).

[0017] The obtained MWW layered precursor and the conversion solution are mixed at a mass ratio of 1: 30 - 100, wherein the molar ratio of the surfactant, organic base and water in the conversion solution is 0.1 - 0.5: 0.5 - 1.0: 30 - 120. After mixing, it is transferred to a crystallization kettle and crystallized at 140 - 170 °C under dynamic crystallization conditions (rotation speed: 15 - 60 rpm) for 36 - 96 hours. After crystallization, the pH value of the mixed solution is adjusted to 10 with 6M H2SO4. The obtained solid sample is filtered, dried and calcined. Subsequently, the solid sample powder is heated to 450 - 550 °C at a heating rate of 1 °C / min in an air atmosphere and calcined at a constant temperature for 2 - 6 hours. Subsequently, ammonium ion exchange and secondary calcination are carried out to obtain a strongly acidic Al-MCM-41 mesoporous catalyst (Al-MCM-41-T-X, where X represents the silicon / aluminum atomic ratio).

[0018] The surfactant is cetyltrimethylammonium bromide (CTAB) or cetyltrimethylammonium chloride (CTACl); the organic base is tetramethylammonium hydroxide (TMAOH) or tetrapropylammonium hydroxide (TPAOH).

[0019] Application of a strongly acidic Al-MCM-41-T mesoporous catalyst prepared by the method, the application of the catalyst in the liquid-phase alkylation reaction of lignin-derived phenols and cycloalcohols / cycloolefins.

[0020] A method for preparing an acidic mesoporous catalyst, the preparation method obtains an Al-MCM-41-T catalyst with a high specific surface area, a high framework aluminum content and strong acidity.

[0021] Compared with the prior art, the present invention provides a method for preparing an Al-MCM-41-T catalyst with a high specific surface area, a concentrated pore distribution and enhanced acidity, having the following advantages and technical effects:

[0022] (1) The present invention uses the MWW layered molecular sieve precursor (i.e., MCM-22(P)) as the silicon and aluminum source, without introducing additional silicon or aluminum sources, and the operation method is simple and controllable.

[0023] (2) The present invention prepares the mesoporous Al-MCM-41-T catalyst with a large specific surface area, concentrated pore distribution and enhanced acidity by the conversion method, effectively improving problems such as the intracrystalline diffusion of macromolecules and the accessibility of strong acid sites in the alkylation reaction.

[0024] (3) By using a clear precursor material (MCM-22(P)) and specific reaction conditions (surfactant concentration, alkali amount, pH value, synthesis temperature, etc.), the method of the present invention can realize the preparation of the Al-MCM-41-T catalyst with a large surface area, concentrated pore distribution and strong acidity. The process is simple and has high repeatability, which is beneficial to large-scale industrial production. Description of the Drawings

[0025] Figure 1 XRD diffraction pattern of the MWW layered molecular sieve precursor (MCM-22(P)) obtained in the examples and comparative examples of the present invention;

[0026] Figure 2 XRD diffraction pattern of Al-MCM-41-T obtained in the examples and comparative examples of the present invention. Among them, a and b are the XRD patterns of the samples after crystallization treatment, and c and d are the XRD patterns of the samples after calcination to remove the surfactant;

[0027] Figure 3 XRD diffraction pattern of Al-MCM-41-C (conventional hydrothermal synthesis method) obtained in Comparative Example 3 of the present invention;

[0028] Figure 4 TEM images of the Al-MCM-41-T catalysts obtained in the examples and Comparative Example 2 of the present invention. Among them, a is Al-MCM-41-T-15, b is Al-MCM-41-T-30, c is Al-MCM-41-T-50, and d is Comparative Example Al-MCM-41-T-80;

[0029] Figure 5 N2 adsorption-desorption isotherm diagrams of the Al-MCM-41-T catalysts obtained in the examples and Comparative Example 2 of the present invention. Among them, a is the N2 adsorption-desorption isotherm curve, and b is the pore size distribution curve diagram;

[0030] Figure 6 N2 adsorption-desorption isotherm diagrams of the Al-MCM-41-C catalysts obtained in the comparative examples of the present invention. Among them, a is the N2 adsorption-desorption isotherm curve, and b is the pore size distribution curve diagram; Detailed Embodiments

[0031] The following further details the specific implementation manners of the present invention in combination with embodiments and the accompanying drawings, so that the technical solution can be more easily understood and mastered. However, the protection scope of the present invention is not limited thereto.

[0032] The present invention uses an MWW layered molecular sieve precursor (i.e., MCM-22(P)) as the only silicon and aluminum source, and prepares an Al-MCM-41-T catalyst with a large specific surface area (exceeding 1000 m 2 g -1 ) and strong acidity through a conversion crystallization method. This process is simple and easy to control, and the acidity of the prepared Al-MCM-41-T can be effectively adjusted by controlling the silicon and aluminum contents in MCM-22(P). When preparing Al-MCM-41-T with a high aluminum content, the conversion crystallization method is adopted in the present invention, which ensures the integrity of the mesoporous framework while greatly increasing the entry of aluminum elements into the MCM-41 framework. The prepared Al-MCM-41-T material with enhanced acidity exhibits high catalytic activity and polyalkylation product selectivity in the liquid-phase alkylation reaction of lignin-derived phenols with cycloalcohols / cycloolefins.

[0033] Example 1:

[0034] Prepare an aluminum-containing MWW layered molecular sieve precursor MCM-22(P)-15 initial gel. Specifically, weigh 0.18 g of sodium aluminate (NaAlO2) and 0.12 g of sodium hydroxide (NaOH) and dissolve them in 20.54 g of deionized water (H2O). Then add 1.52 g of hexamethyleneimine (HMI) and stir evenly. Finally, add 6.15 g of silica sol (SiO2) and stir well. The molar ratio of the solution system is SiO2:Al2O3:Na2O:HMI:H2O = 1:0.033:0.1:0.5:44. Transfer the obtained initial gel to a crystallization kettle, age it at 90 °C for 12 hours, and then crystallize it at 160 °C for 120 hours under dynamic conditions (rotation speed: 20 rpm). Filter and wash the solid obtained after crystallization, and dry it at 80 °C for 12 hours to obtain the MCM-22(P) molecular sieve precursor, denoted as MCM-22(P)-15, where 15 represents the silicon / aluminum atomic ratio (see Figure 1 ).

[0035] 1.38g of hexadecyltrimethylammonium bromide (CTAB) and 8.8g of 25wt% tetrapropylammonium hydroxide (TPAOH) were completely dissolved in 16g of deionized water at 40°C, and the solution pH was 13. Then, the MCM-22(P) precursor obtained in Example 1 was added thereto, and then stirring was continued for 1 hour. Then, the mixture was transferred to a crystallization kettle and crystallized at 150°C for 72 hours under dynamic conditions (rotation speed: 40rpm). The solid obtained after crystallization was adjusted to pH 10 with 6M H2SO4 solution, and then filtered and washed, and dried at 80°C for 12 hours. The obtained sample was heated to 550°C at a heating rate of 1°C / min in an air atmosphere, and calcined at a constant temperature for 6 hours. After ion exchange (0.5M ammonium acetate, 60°C, 6 hours) and secondary calcination (400-450°C, constant temperature calcination for 6 hours), the obtained solid was recorded as Al-MCM-41-T-15, where 15 represents the silicon / aluminum atomic ratio (see Figure 2 , 4 , 5).

[0036] Embodiment 2:

[0037] The initial gel of aluminum-containing MWW layered molecular sieve precursor MCM-22(P)-30 was prepared. Specifically, 0.09g sodium aluminate (NaAlO2) and 0.12g sodium hydroxide (NaOH) were weighed and dissolved in 20.54g deionized water (H2O), then 1.52g hexamethyleneimine (HMI) was added and stirred evenly, and finally 6.15g silica sol (SiO2) was added and stirred thoroughly, and the molar ratio of the solution system was SiO2:Al2O3:Na2O:HMI:H2O=1:0.017:0.1:0.5:44. The obtained initial gel was transferred to a crystallization reactor and aged at 90°C for 12 hours, and then crystallized at 160°C for 120 hours under dynamic conditions (rotation speed: 20 rpm). The solid obtained after crystallization was filtered and washed, and dried at 80°C for 12 hours to obtain the MCM-22(P) molecular sieve precursor, which was denoted as MCM-22(P)-30, where 30 represents the silicon / aluminum atomic ratio (see Figure 1 ).

[0038] 1.38 g of cetyltrimethylammonium bromide (CTAB) and 8.8 g of 25 wt% tetrapropylammonium hydroxide (TPAOH) were completely dissolved in 16 g of deionized water at 40 °C. The pH value of the solution was 13. Subsequently, the MCM-22(P) precursor obtained in Example 1 was added thereto, and then stirring was continued for 1 hour. Then, it was transferred to a crystallization kettle and crystallized at 150 °C for 72 hours under dynamic conditions (rotation speed: 40 rpm). The pH value of the solid obtained after crystallization was adjusted to 10 with 6 M H2SO4 solution, and then suction filtration and washing were carried out, and it was dried at 80 °C for 12 hours. The obtained sample was heated to 550 °C at a heating rate of 1 °C / min in an air atmosphere and calcined at a constant temperature for 6 hours. The solid obtained after ion exchange (0.5 M ammonium acetate, 60 °C, 6 hours) and secondary calcination (400 - 450 °C, calcined at a constant temperature for 6 hours) was denoted as Al-MCM-41-T-30, and 30 represents the silicon / aluminum atomic ratio (see Figure 2 , 4 , 5).

[0039] Example 3:

[0040] Prepare an aluminosilicate MWW layered zeolite precursor MCM-22(P)-50 initial gel. Specifically, 0.05 g of sodium aluminate (NaAlO2) and 0.12 g of sodium hydroxide (NaOH) were dissolved in 20.54 g of deionized water (H2O). Subsequently, 1.52 g of hexamethyleneimine (HMI) was added and stirred evenly, and finally 6.15 g of silica sol (SiO2) was added and stirred thoroughly. The molar ratio of the solution system was SiO2:Al2O3:Na2O:HMI:H2O = 1:0.01:0.1:0.5:44. The obtained initial gel was transferred to a crystallization kettle and aged at 90 °C for 12 hours, and then crystallized at 160 °C for 120 hours under dynamic conditions (rotation speed: 20 rpm). The solid obtained after crystallization was suction filtered and washed, and dried at 80 °C for 12 hours to obtain the MCM-22(P) zeolite precursor, denoted as MCM-22(P)-50, and 50 represents the silicon / aluminum atomic ratio (see Figure 1 ).

[0041] 1.38 g of cetyltrimethylammonium bromide (CTAB) and 8.8 g of 25 wt% tetrapropylammonium hydroxide (TPAOH) were completely dissolved in 16 g of deionized water at 40 °C. The pH value of the solution was 13. Subsequently, the MCM-22(P) precursor obtained in Example 1 was added thereto, and then stirring was continued for 1 hour. Then, it was transferred to a crystallization kettle and crystallized at 150 °C for 72 hours under dynamic conditions (rotation speed: 40 rpm). The pH value of the solid obtained after crystallization was adjusted to 10 with 6 M H2SO4 solution, and then it was filtered and washed, and dried at 80 °C for 12 hours. The obtained sample was heated to 550 °C at a heating rate of 1 °C / min in an air atmosphere and calcined at a constant temperature for 6 hours. The solid obtained after ion exchange (0.5 M ammonium acetate, 60 °C, 6 hours) and secondary calcination (400 - 450 °C, calcined at a constant temperature for 6 hours) was denoted as Al-MCM-41-T-50, and 50 represents the silicon / aluminum atomic ratio (see Figure 2 , 4 , 5).

[0042] Comparative Example 1:

[0043] Preparation of the precursor MCM-22(P)-10 of the aluminosilicate MWW layered molecular sieve containing aluminum: 0.25 g of sodium aluminate (NaAlO2) and 0.12 g of sodium hydroxide (NaOH) were dissolved in 20.54 g of deionized water (H2O). Subsequently, 1.52 g of hexamethyleneimine (HMI) was added and stirred evenly. Finally, 6.15 g of silica sol (SiO2) was added and stirred thoroughly. The molar ratio of the solution system was SiO2:Al2O3:Na2O:HMI:H2O = 1:0.05:0.1:0.5:44. The obtained initial gel was transferred to a crystallization kettle and aged at 90 °C for 12 hours, and then crystallized at 160 °C for 120 hours under dynamic conditions (rotation speed: 20 rpm). The solid obtained after crystallization was filtered and washed, and dried at 80 °C for 12 hours to obtain the MCM-22(P) molecular sieve precursor, denoted as MCM-22(P)-10, and 10 represents the silicon / aluminum atomic ratio (see Figure 1 ).

[0044] Comparative Example 2:

[0045] Preparation of the initial gel for the aluminosilicate MWW zeolite precursor MCM-22(P)-80: Weigh 0.025 g of sodium aluminate (NaAlO2) and 0.12 g of sodium hydroxide (NaOH) and dissolve them in 20.54 g of deionized water (H2O). Subsequently, add 1.52 g of hexamethyleneimine (HMI) and stir well. Finally, add 6.15 g of silica sol (SiO2) and stir thoroughly. The molar ratio of the solution system is SiO2:Al2O3:Na2O:HMI:H2O = 1:0.006:0.1:0.5:44. Transfer the obtained initial gel to a crystallization kettle, age it at 90 °C for 12 hours, and then crystallize it at 160 °C for 120 hours under dynamic conditions (rotation speed: 20 rpm). Filter and wash the solid obtained after crystallization, and dry it at 80 °C for 12 hours to obtain the MCM-22(P) zeolite precursor, denoted as MCM-22(P)-80, where 80 represents the silicon / aluminum atomic ratio (see Figure 1 ).

[0046] Dissolve 1.38 g of cetyltrimethylammonium bromide (CTAB) and 8.8 g of 25 wt% tetrapropylammonium hydroxide (TPAOH) in 16 g of deionized water at 40 °C. The pH value of the solution is 13. Subsequently, add the MCM-22(P) precursor obtained in Example 1, continue to stir for 1 hour, and then transfer it to a crystallization kettle and crystallize it at 150 °C for 72 hours under dynamic conditions (rotation speed: 40 rpm). Adjust the pH value of the solid obtained after crystallization to 10 with 6M H2SO4 solution, then filter and wash it, and dry it at 80 °C for 12 hours. Heat the obtained sample to 550 °C at a heating rate of 1 °C / min in an air atmosphere and calcine it at a constant temperature for 6 hours. The solid obtained after ion exchange (0.5M ammonium acetate, 60 °C, 6 hours) and secondary calcination (400 - 450 °C, calcined at a constant temperature for 6 hours) is denoted as Al-MCM-41-T-80, where 80 represents the silicon / aluminum atomic ratio (see Figure 2 , 4 , 5).

[0047] Comparative Example 3:

[0048] The Al-MCM-41 material was prepared by a conventional hydrothermal synthesis method [Appl. Catal., A 1997, 161, 1-2, 121-127; Microporous Mesoporous Mater. 2001, 43, 171-179], labeled as Al-MCM-41-C, with a silicon / aluminum atomic ratio of 22 (determined by X-ray fluorescence spectrometer). The specific synthesis method: 6.07 g of cetyltrimethylammonium bromide (CTAB) and 1.52 g of tetramethylammonium hydroxide (TMAOH) were completely dissolved in 18 g of deionized water at 40 °C. Subsequently, 1 g of silica and 0.09 g of NaAlO2 were added thereto, and then stirring was continued for 1 hour. Then it was transferred to a crystallization kettle and crystallized at 100 °C for 72 hours. The pH value of the solid obtained after crystallization was adjusted to 10 with 6M H2SO4 solution, and then filtered and washed, and dried at 80 °C for 12 hours. The obtained sample was heated to 550 °C at a heating rate of 1 °C / min in an air atmosphere and calcined at a constant temperature for 6 hours. The solid obtained after ion exchange (0.5M ammonium acetate, 60 °C, 6 hours) and secondary calcination (400-450 °C, calcined at a constant temperature for 6 hours) was denoted as Al-MCM-41-C (see Figure 3 , 6 ).

[0049] The samples obtained in the above examples and comparative examples were characterized and tested: XRD tests were respectively carried out on the MCM-22(P) molecular sieve precursor used and the Al-MCM-41-T sample obtained after conversion, and XRD diffraction patterns were obtained, as shown in Figure 1 and Figure 2 . In the synthesized silica-aluminum MCM-22(P) molecular sieve precursor sample, only the XRD peak shapes with a silicon / aluminum atomic ratio of 15-80 were consistent with the XRD peak shapes of the MWW layered structure molecular sieve reported in the literature (see Figure 1) It indicates that a highly crystalline MCM-22(P) zeolite precursor with a silicon / aluminum ratio of 15 - 80 was successfully synthesized without any impurity phases. For the synthesis of MWW precursors with lower silicon / aluminum ratios, obvious impurity peaks were observed in the XRD patterns of the obtained MCM-22(P)-10 samples, indicating the formation of other crystal phases under these crystallization conditions, which is consistent with the reports in the literature [Microporous Mesoporous Mater. 2006, 97, 78 - 87; Microporous Mesoporous Mater. 2009, 118, 1 - 3, 1 - 10]. Since the crystal phase of MCM-22(P)-10 was impure, no phase conversion treatment was carried out on it subsequently. After the phase conversion of the MCM-22(P)-X (X = 15 - 80) precursor samples, obvious diffraction peaks were observed in the Al-MCM-41-T samples between 2θ = 1.6 - 3, which are characteristic diffraction peaks of the (100) crystal plane with hexagonal pores. Moreover, no diffraction peaks of MWW zeolite crystals or other impurity peaks were found in either the wide-angle or small-angle XRD patterns, indicating that the phase conversion method used successfully obtained a single MCM-41 mesoporous phase structure with an ordered and regular mesoporous structure (see Figure 2 a - Small-angle XRD, 2b - Wide-angle XRD). In addition, the XRD results after air calcination showed that after removing the surfactant, the hexagonal pore structure of all Al-MCM-41-T samples could still exist stably (see Figure 2 c - Small-angle XRD of the calcined sample, 2d - Wide-angle XRD of the calcined sample). Figure 3 The small-angle and wide-angle XRD patterns of the comparative Al-MCM-41-C sample are given, indicating that this sample has good mesoporous order, which is consistent with the literature reports.

[0050] TEM characterization of the obtained samples showed that all the phase-converted Al-MCM-41-T had regular hexagonal mesoporous array structures (see Figure 4 ). Figure 5 The N2 adsorption - desorption isotherm and pore size distribution diagrams of Al-MCM-41-T are given. It belongs to the adsorption curve of typical mesoporous materials. Combining with the pore size distribution diagram, it shows that the phase-converted Al-MCM-41 catalyst has a higher mesoporous capacity and a concentrated mesoporous pore size distribution, and has a slightly larger pore size (3.1 vs 2.7 nm) than the comparative Al-MCM-41-C sample (see Figure 6 ). Table 1 gives the specific pore structure parameters. The specific surface areas of the phase-converted Al-MCM-41-T catalysts all exceed 1000 m 2 g -1 , and the mesoporous pore volumes all exceed 1.2 cm 3 g -1 , far exceeding the pore structure parameters of the samples obtained under conventional hydrothermal conditions.

[0051] Table 1. Pore structure parameters of Al-MCM-41-T and Al-MCM-41-C samples

[0052]

[0053] To obtain the acidic properties of the materials, pyridine infrared (Py-FTIR) tests were carried out on the phase-transformed Al-MCM-41-T and the comparative Al-MCM-41-C. The amounts of pyridine desorbed at 150 °C and 400 °C were used to determine the total acid amount and the strong acid amount, respectively (Table 2). Although the silicon / aluminum ratio of the comparative sample was the lowest, the total Brønsted acid amount (BAS total ) and the strong Brønsted acid amount (BAS trong ) of the phase-transformed Al-MCM-41-T sample were higher than those of the comparative Al-MCM-C sample.

[0054] Table 2. Acidic characterization data of Al-MCM-41-T and Al-MCM-41-C samples

[0055]

[0056] Lignin-derived phenolic compounds are expected to replace traditional fossil resources through catalytic upgrading to produce high-value fuels and chemicals. The alkylation process through the acid-catalyzed carbon-carbon coupling process is a key technology for upgrading biomass to prepare high-density fuels. The alkylation reactions of phenol-cyclohexanol (the hydrogenation product of phenol) and 4-cyclohexylphenol-cyclohexene (the dehydration product of cyclohexanol) were used as probes to compare the performance of the phase-transformed Al-MCM-41-T and the comparative Al-MCM-41-C catalysts.

[0057] Specifically:

[0058] The alkylation reactions of phenol and cyclohexanol were catalyzed by the obtained Al-MCM-41-T-15, 30, and 50 in the above examples and the comparative Al-MCM-41-C catalyst, respectively, and carried out in a batch sealed stainless-steel reactor. The reactants (2.0 g of phenol and 2.0 g of cyclohexanol), 0.5 g of the catalyst, and 100 mL of n-dodecane were added to the reactor, and then the reactor was purged three times with 2 MPa of N2 and filled with 3 MPa of N2. Then, the reactor was heated to 160 °C under stirring conditions (rotation speed: 700 rpm). When the temperature reached 160 °C, it was regarded as the zero point of the reaction. The reaction was carried out for 480 minutes and the products were analyzed on a gas chromatography / mass spectrometry instrument (see Table 3).

[0059] As can be seen above, after 480 minutes of reaction, the Al-MCM-41-T-15 catalyst showed the highest phenol conversion rate (74%), while the phenol conversion rate on the comparative Al-MCM-41-C was only 18% under the same conditions. The alkylation reaction activity order of the investigated catalysts was: Al-MCM-41-T-15 > Al-MCM-41-T-30 > Al-MCM-41-T-50 > Al-MCM-41-T-80 ≥ Al-MCM-41-C. Compared with the comparative Al-MCM-41-C catalyst, the improvement in alkylation activity on the samples obtained by the crystal transformation can be attributed to the enhanced Bronsted acidity (high acid site concentration and strength). The phenol conversion rate and the yield of alkylation products on the samples obtained by the crystal transformation were significantly correlated with the silicon / aluminum ratio of the catalyst, that is, related to the acidity of the catalyst. Among them, the Al-MCM-41-T-80 sample had little difference in phenol conversion rate and alkylation activity from Al-MCM-41-C, and could not highlight the advantages of the crystal transformation method. Therefore, we limited the silicon / aluminum ratio to 15 - 50 by the crystal transformation method.

[0060] To further verify the advantages of the crystal transformation samples in the alkylation performance of larger molecules, we compared the alkylation performance of the Al-MCM-41-T-15 and Al-MCM-41-C catalysts in the alkylation of 4-cyclohexylphenol with cyclohexene. The reaction conditions were: 2.0 g of 4-cyclohexylphenol, 4.7 g of cyclohexene, 0.5 g of catalyst, 100 mL of n-dodecane, 3 MPa of N2, a rotation speed of 700 rpm, a reaction temperature of 160 °C, and a reaction time of 480 minutes. The results showed that the Al-MCM-41-T-15 catalyst not only had a higher conversion rate of 4-cyclohexylphenol than Al-MCM-41-C (100% vs 83%), but also had a more obvious gap in the selectivity of alkylation products. Specifically, mainly tri-substituted polyalkylated products (Tri-C-alkylates) were formed on the Al-MCM-41-T-15 catalyst with a selectivity as high as 88%, while the main alkylation product on Al-MCM-41-C was di-substituted alkylated products (Di-C-alkylates) with a selectivity of 67%. The higher alkylation activity on Al-MCM-41-T-15 can be attributed to its enhanced acidity and larger mesoporous structure, which again verified the advantages of the crystal transformation method in the synthesis of Al-MCM-41 materials.

[0061] Table 3. Conversion rates and main product distributions of the alkylation reactions of phenol - cyclohexanol and 4-cyclohexylphenol - cyclohexene catalyzed by the examples of the present invention

[0062]

[0063] In summary, the present invention uses the MWW layered zeolite precursor (i.e., MCM-22(P)) as the sole silicon and aluminum source. Through the conversion method, the primary structure units of zeolite in the MCM-22(P) precursor are embedded in the Al-MCM-41 material by the assembly action of surfactants, greatly enhancing the acid concentration and acid strength of mesoporous Al-MCM-41. It shows excellent catalytic activity and selectivity for polyalkylation products during the catalytic alkylation reaction of lignin-derived phenol-cyclohexanol and 4-cyclohexylphenol-cyclohexene, and has potential advantages in the value-added conversion of lignin-based biomass.

[0064] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst, characterized in that: Using aluminum-containing MWW layered molecular sieve precursor (i.e., MCM-22(P)) as raw material, an Al-MCM-41-T catalyst with large surface area, high framework aluminum content and strong acidity was prepared by a crystal rotation method.

2. The method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst according to claim 1, characterized in that: (1) Preparation of MWW layered precursors; (2) dispersing the layered precursor in an alkaline solution containing a surfactant and stirring the solution evenly; (3) placing the above-obtained solution in a hydrothermal reactor for crystallization treatment; (4) The crystallized sample is washed, dried, calcined, and subjected to ammonium ion exchange and secondary calcination to obtain a strongly acidic Al-MCM-41-T material.

3. The method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst according to claim 2, characterized in that: The preparation of the MWW layered molecular sieve precursor is as follows: a silicon source, an aluminum source, a template and an alkali source are dissolved in water and stirred evenly, then transferred to a crystallization kettle for crystallization treatment, and then washed and dried to obtain an MCM-22 (P) precursor; wherein the silicon / aluminum atomic ratio in the precursor feed system is 15-50.

4. The method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst according to claim 3, characterized in that: In the preparation of the MCM-22 (P) precursor, the molar ratio of silicon source, aluminum source, template, alkali source and water is 1.0: 0.008-0.035: 0.3-0.8: 0.05-0.3: 30-80, the crystallization treatment conditions are 140-170° C., and the rotation speed is 15-60 rpm.

5. The method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst according to claim 4, characterized in that: In the preparation of the MCM-22(P) precursor, the silicon source is silica sol, white carbon black, tetraethyl orthosilicate (TEOS); the aluminum source is sodium aluminate (NaAlO2), aluminum sulfate (Al2(SO4)3), aluminum isopropoxide (C9H 21 AlO3).

6. The method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst according to claim 2, characterized in that: The obtained MWW layered precursor is mixed with a crystallization solution in a mass ratio of 1:30-100, wherein the molar ratio of the surfactant, the organic base and the water in the crystallization solution is 0.1-0.5:0.5-1.0:30-120, and the mixture is transferred to a crystallization kettle for crystallization for 36-96 hours at 140-170°C under dynamic crystallization conditions (rotation speed: 15-60rpm). After crystallization, the pH value of the mixed solution is adjusted to 10 with 6M H2SO4, and the obtained solid sample is filtered, dried and calcined. Subsequently, the solid sample powder is heated to 450-550°C at a heating rate of 1°C / min in an air atmosphere, and calcined at a constant temperature for 2-6 hours, followed by ammonium ion exchange and secondary calcination to obtain a strongly acidic Al-MCM-41 mesoporous catalyst (Al-MCM-41-TX, wherein X represents the silicon / aluminum atomic ratio).

7. The method for preparing a strongly acidic Al-MCM-41 mesoporous catalyst according to claim 6, characterized in that: The surfactant is hexadecyltrimethylammonium bromide (CTAB) or hexadecyltrimethylammonium chloride (CTACl); the organic base is tetramethylammonium hydroxide (TMAOH) or tetrapropylammonium hydroxide (TPAOH).

8. An application of the strongly acidic Al-MCM-41-T mesoporous catalyst prepared by the method of claim 1, characterized in that: The catalyst is used in the liquid phase alkylation reaction of lignin-derived phenols and cyclic alcohols / cyclic alkenes.

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