Preparation of activated carbon supported solid superacid catalyst and its application in hydrogenolysis of c-o bond in aryl ethers

Abstract

The application discloses a preparation of an activated carbon supported solid superacid catalyst and application of the catalyst in C-O bond hydrogenolysis of aryl ethers. 2‑ The metal ruthenium, ZrO2 and S2O8 2‑ are loaded on the carrier by an impregnation method to obtain a high-activity solid superacid Ru-SO / xZr-AC (x=5, 10, 15 or 20) catalyst; the metal ruthenium is uniformly distributed on the carrier, the average size of the metal particles in the Ru-SO / 10Zr-AC catalyst is significantly reduced to 1.68 nm compared with that in the Ru / AC; compared with other Ru-based catalysts, the Ru-SO / 10Zr-AC solid superacid catalyst has the highest activity in C-O bond hydrogenolysis of diphenyl ether and exhibits the highest catalytic performance, and can control the high-efficiency conversion of diphenyl ether into monocyclic products under the optimal reaction conditions (180 DEG C, 1 MPa H2, 2 h and n-hexane). The high-activity solid superacid Ru-SO / xZr-AC catalyst provided by the application can efficiently catalyze the C-O bond hydrogenolysis of diphenyl ether and other aryl ethers while inhibiting the hydrogenation of aromatic rings, greatly saves the cost, is safer and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a solid acid catalyst, in particular to a preparation of an activated carbon supported solid superacid catalyst and its application in the hydrogenolysis of aromatic ether C-O bond, belonging to the technical field of catalysts. BACKGROUND

[0002] Lignin, as one of the three major components of lignocellulosic biomass, is considered as the most promising and sustainable resource for obtaining high value-added chemicals and biofuels. It is well known that there are a large number of C-O bonds in the molecular structure of lignin, mainly including α-O-4, β-O-4 and 4-O-5 ether bonds. Among them, the 4-O-5 ether bond is the strongest C-O bond in lignin, therefore, selectively cleaving the C-O bond in the 4-O-5 bond is of great significance for the depolymerization of lignin, and diphenyl ether is a typical model compound of 4-O-5 bond.

[0003] Solid heterogeneous catalysts with high activity are the best choice for lignin conversion. A large number of Ni, Co, Pd, Ru and Pt-based heterogeneous catalysts have been rapidly developed for the hydrogenolysis of diphenyl ether. Among them, Ru-based catalysts exhibit excellent performance in the hydrogenolysis of C-O bond because of their high activity for H2 dissociation, especially Ru / AC catalysts are most widely used. Although Ru / AC catalysts have very high activity for the cleavage of aromatic ether C-O bond, they can also cause serious hydrogenation, even the cleavage of carbon skeleton. Controlling Ru / AC for the direct hydrogenolysis of C-O bond in diphenyl ether to avoid the continuous hydrogenation of aromatic ring has become one of the main research challenges in the field of catalyst design. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of an activated carbon supported solid superacid catalyst, and to prepare a new high-activity Ru-based catalyst.

[0005] The second purpose of the present application is to provide the application of the activated carbon supported solid superacid catalyst prepared by the above preparation method in the hydrogenolysis of aromatic ether C-O bond.

[0006] To achieve the above purposes, the technical solutions adopted by the present application are as follows:

[0007] On the one hand, the present application provides a preparation method of an activated carbon supported solid superacid catalyst, comprising the following steps:

[0008] (1) preparing a zirconium oxide precursor aqueous solution, then adding activated carbon powder, and after ultrasonic stirring for 5-10 min, the mixture is immersed at room temperature for 10-12 h;

[0009] (2) after the immersion is completed, under stirring conditions, ammonia water is added to adjust the pH value of the solution to 9-10, so that a precipitate is generated, and the precipitate is aged at room temperature for 10-12 h;

[0010] (3) Filter, wash the precipitate with water until no Cl - exists, dry to obtain a solid powder containing amorphous Zr(OH)4;

[0011] (4) Put the solid powder containing amorphous Zr(OH)4 into a 1 mol / L ammonium persulfate solution, stir for 2 h first, then immerse at room temperature for 6 h, after the immersion is completed, filter and dry;

[0012] (5) Put the sample dried in step (4) into a tube furnace, calcine at 550℃ for 3 h under an argon atmosphere, and obtain a solid marked as SO / Zr-AC;

[0013] (6) Prepare an aqueous solution of a ruthenium precursor, after stirring for 5-15 min, add the SO / Zr-AC obtained in step (5), and ultrasonic for 15-30 min; immerse the mixed solution in a vacuum drying box for 24 h, after the immersion is completed, dry the mixture; wherein the ruthenium loading is 5 wt.%;

[0014] (7) Put the sample dried in step (6) into a tube furnace, calcine at 300℃ for 2 h under an argon atmosphere, and then reduce at 300℃ under hydrogen with the same flow rate for 2 h; after calcination and reduction, switch to argon to cool to room temperature, and obtain a Ru-SO / Zr-AC catalyst.

[0015] Preferably, the zirconium precursor in step (1) is zirconium oxychloride octahydrate, and the ruthenium precursor in step (6) is ruthenium trichloride.

[0016] Preferably, the amount of zirconia in the zirconium precursor in step (2) is 5-20% of the amount of the Zr-AC carrier.

[0017] Preferably, the drying temperature in steps (3), (4), and (6) is all 110℃, and the drying time is all 12 h.

[0018] Preferably, the argon flow rate in step (5) is 200 mL / min, and the argon flow rate in step (7) is 70 mL / min.

[0019] Preferably, the temperature rising rate in step (5) is 10℃ / min, and the temperature rising rate in step (7) is 15℃ / min.

[0020] In a second aspect, the application provides the use of the activated carbon supported solid superacid catalyst prepared by the above preparation method in the hydrogenolysis of aryl ether C-O bonds.

[0021] The steps of specific application include: putting the reaction substrate aryl ether, the catalyst and n-hexane into a reactor, replacing three times of air with hydrogen after sealing; then, pressurizing the reactor to 1 MPa with hydrogen at room temperature; then, increasing the temperature to 180-240 DEG C, and stirring vigorously for 1-4 h; after the experiment, cooling the reaction system to room temperature naturally and releasing the pressure. The reaction mixture is filtered to remove the catalyst, and the organic phase is obtained by gas chromatography and gas phase analysis.

[0022] Preferably, the catalyst accounts for 30% of the mass proportion of the substrate.

[0023] Preferably, the substrate aryl ether is any one of diphenyl ether, benzyl phenyl ether, p-xylene ether, 4-phenoxyphenol, and dibenzyl ether.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1. The present application first prepares a zirconium-based solid superacid carrier loaded with activated carbon (AC), and then continues to prepare a solid superacid Ru-SO / xZr-AC catalyst loaded with Ru. By utilizing the unique advantages of the superacid itself, the direct cleavage of the C-O bond in diphenyl ether can be significantly controlled, and the hydrogenation of the aromatic ring is inhibited, so that a large amount of single-ring target product cleaved from the C-O bond is finally generated.

[0026] 2. In the catalyst of the present application, the metal ruthenium is uniformly distributed on the carrier. Compared with Ru / AC, the average size of the metal particles in the Ru-SO / 10Zr-AC catalyst is significantly reduced to 1.68 nm. Compared with other Ru-based catalysts, the Ru-SO / 10Zr-AC solid superacid catalyst has the highest activity for the hydrogenolysis of the C-O bond in diphenyl ether, and exhibits the highest catalytic performance. Under the optimal reaction conditions (180 DEG C, 1 MPa H2, 2 h, and n-hexane), diphenyl ether can be efficiently converted into a single-ring product by controlling the hydrogenolysis of the C-O bond. The high-activity solid superacid Ru-SO / xZr-AC catalyst provided by the present application can efficiently catalyze the hydrogenolysis of the C-O bond in diphenyl ether while inhibiting the hydrogenation of the aromatic ring, and is also applicable to the hydrogenation and cleavage of the C-O bond in other lignin model compounds. Therefore, the cost is greatly saved, the safety is higher, and the catalyst has a good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the NH3-TPD curve of the catalyst prepared in Examples 1-4 of the present application;

[0028] Figure 2 is the SEM image of the catalyst prepared in Examples 1-4 of the present application;

[0029] Figure 3 is the TEM image and the corresponding particle size distribution graph of the catalyst prepared in Examples 1-4 of the present application;

[0030] Figure 4 Figure 1 is an XRD spectrum of the solid superacid catalyst prepared in Example 1 of the present application;

[0031] Figure 5 Figure 2 is an XPS spectrum of the solid superacid catalyst prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described in conjunction with the accompanying drawings and specific examples.

[0033] Example 1, Synthesis of solid superacid Ru-SO / 10Zr-AC catalyst by impregnation method

[0034] A solid superacid Ru-SO / 10Zr-AC catalyst was synthesized by impregnation method. 1.4555 g of zirconium oxychloride (ZrOCl2·8H2O) was weighed into a beaker, 15 mL of deionized water was added, and the mixture was stirred by ultrasound for 5 min to dissolve. 5 g of commercial activated carbon (AC) powder was added to the beaker, and the mixture was stirred by ultrasound for 5 min. After completion, the mixture was immersed at room temperature for 10 h. After the immersion was completed, an appropriate amount of ammonia water was added under magnetic stirring to adjust the pH of the solution to 9-10 to cause precipitation, and the mixture was aged at room temperature for 12 h. The mixture was suction filtered and washed with deionized water until no Cl - was detected (determined by AgNO3), and then dried in an oven at 110°C for 12 h to obtain a solid powder containing amorphous Zr(OH)4. The solid powder containing amorphous Zr(OH)4 was placed in a 20 mL solution of ammonium persulfate ((NH4)2S2O8) with a concentration of 1 mol / L. The mixture was stirred for 2 h, and then immersed at room temperature for 6 h. The obtained solid was dried in an oven at 110°C for 12 h. After the drying was completed, the sample was placed in a tube furnace and calcined. Argon gas with a flow rate of 200 mL / min was introduced, and the temperature was raised to 550°C at a rate of 10°C / min, and then maintained at 550°C for 3 h. The obtained solid was labeled as SO / 10Zr-AC.

[0035] In a typical experiment, 0.108 g of the metal salt ruthenium precursor, ruthenium trichloride hydrate (RuCl3-xH2O) was dissolved in a beaker with a proper amount of deionized water. After stirring for 5-15 min, 1 g of SO / 10Zr-AC support was added into the aqueous solution and ultrasonicated for 15-30 min. Then, the mixed solution was impregnated in a vacuum drying oven for 24 h. After the impregnation, the mixture was dried in a drying oven at 110 °C for 12 h, calcined at 300 °C for 2 h under an argon flow of 70 mL / min, and then reduced at 300 °C under hydrogen at the same flow for 2 h, with a heating rate of 15 °C / min. After the calcination and reduction, the flow was switched back to argon to cool down to room temperature to obtain the Ru-SO / 10Zr-AC catalyst.

[0036] Example 2, synthesis of solid superacid Ru-SO / 5Zr-AC catalyst by impregnation method

[0037] The preparation method of this example is basically the same as that of Example 1, except that the mass of ZrOCl2-8H2O added is 0.6895 g, and the loading of Ru is 5 wt.%.

[0038] Example 3, synthesis of solid superacid Ru-SO / 15Zr-AC catalyst by impregnation method

[0039] The preparation method of this example is basically the same as that of Example 1, except that the mass of ZrOCl2-8H2O added is 2.3117 g, and the loading of Ru is 5 wt.%.

[0040] Example 4, synthesis of solid superacid Ru-SO / 20Zr-AC catalyst by impregnation method

[0041] The preparation method of this example is basically the same as that of Example 1, except that the mass of ZrOCl2-8H2O added is 3.2749 g, and the loading of Ru is 5 wt.%.

[0042] Table 1 pore structure characteristics of different catalysts

[0043]

[0044]

[0045] S BET : total specific surface area; V total : total pore volume; D ave : average pore diameter.

[0046] The pore structure information of the Ru-SO / xZr-AC solid superacid catalyst is shown in Table 1. The catalyst shows typical porosity, and there are a large number of micropores and mesopores in the catalyst. With the loading of zirconium metal, the total specific surface area and total pore volume of the catalyst show a gradually decreasing trend.

[0047] As shown in Figure 1 , NH3-TPD characterization shows that the Ru-SO / xZr-AC solid superacid catalyst has strong acidity. At a temperature of 600-900℃, two obvious desorption peaks appear, indicating that the Ru-SO / xZr-AC catalyst is a solid superacid catalyst. With the increase of the loading amount of zirconium metal, the corresponding desorption temperature shifts to the high temperature zone, indicating that the solid superacid catalyst has stronger acidity.

[0048] As shown in Figure 2 , SEM characterization shows that the Ru-SO / xZr-AC solid superacid catalyst still has the typical pore structure characteristics of activated carbon. However, with the increase of the loading amount of zirconium metal, the corresponding pore channels will be gradually occupied by the metal. When the loading amount of zirconium metal is greater than 10%wt, the loaded metal will adhere to the surface of the activated carbon support.

[0049] As shown in Figure 3 , TEM characterization shows that the metal particles of Ru / AC and Ru-SO / 10Zr-AC solid superacid catalysts are highly dispersed, and the corresponding average particle size of the metal is 1.82nm and 1.68nm, respectively. Compared with Ru / AC, the average particle size of the metal in Ru-SO / 10Zr-AC solid superacid catalyst is significantly reduced.

[0050] As shown in Figure 4 , XRD characterization shows that the characteristic diffraction peaks of ruthenium metal in Ru / AC and Ru-SO / xZr-AC solid superacid catalysts are very weak and almost cannot be observed, indicating that the ruthenium metal is highly dispersed. The Ru-SO / xZr-AC solid superacid catalyst shows obvious characteristic diffraction peaks at 2 values of 30.40°, 35.25°, 50.71° and 60.28°, which are respectively attributed to the (111), (200), (220) and (311) crystal faces of ZrO2, confirming that the zirconium on the surface of the activated carbon exists in the form of ZrO2.

[0051] As shown in Figure 5 , XPS characterization shows that the ruthenium in Ru / AC and Ru-SO / xZr-AC solid superacid catalysts shows corresponding peak intensity at a bond energy of 484.8eV and 462.7eV, which belongs to the metallic state of ruthenium, indicating that the valence state of the metal ruthenium in Ru / AC and Ru-SO / xZr-AC solid superacid catalysts is completely the same.

[0052] Example 5, Hydrogenation application of Ru-SO / xZr-AC solid superacid catalysts

[0053] The catalytic reaction of diphenyl ether was taken as an example:

[0054] All catalytic reactions were carried out in a 100 mL stainless steel autoclave. In a typical experiment, 0.1 g of the reaction substrate (diphenyl ether), a certain amount of catalyst (30 mg) and n-hexane (20 mL) were placed in the reactor. After sealing, residual air was removed by purging with hydrogen gas 3 times. Subsequently, the reactor was pressurized with hydrogen gas to the desired pressure (1 MPa) at room temperature. The temperature was then raised to the desired reaction temperature (180 °C) and maintained for a certain time (1 h) at a vigorous stirring speed of 800 rpm. After the experiment was completed, the reaction system was naturally cooled to room temperature and the pressure was released. The reaction mixture was filtered to remove the catalyst, and the obtained organic phase was analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC).

[0055] Table 2 Hydrogenation catalytic conversion performance of different catalysts on diphenyl ether

[0056]

[0057] Reaction conditions: 0.1 g of diphenyl ether, 30 mg of catalyst, 20 mL of n-hexane, 180 °C, 1 h, 1 MPa H2. M = AC, SO / 5Zr-AC, SO / 10Zr-AC, SO / 15Zr-AC and SO / 20Zr-AC.

[0058] Table 2 summarizes the results of the hydrogenation conversion reaction of diphenyl ether by different solid superacid Ru-SO / xZr-AC catalysts. Obviously, when no catalyst is added or only the SO / xZr-AC carrier is present, diphenyl ether is not hydrogenated under the reaction conditions studied, while after adding the prepared Ru / AC and Ru-SO / xZr-AC solid superacid catalysts, diphenyl ether shows different degrees of conversion. Under the reaction conditions studied, the prepared Ru / AC catalyst can completely convert diphenyl ether with a conversion rate of 100%, and the products generated are cyclohexane, cyclohexanol and oxydicyclohexane, and there are also many aromatic ring hydrogenation products oxydicyclohexane in addition to the cleavage of diphenyl ether. Under the same conditions, when Ru-SO / xZr-AC solid superacid catalysts are added, the conversion rate of diphenyl ether decreases, among which Ru-SO / 10Zr-AC has a conversion rate of 91.2%, but in terms of product distribution, the yield of C-O bond cleavage products of diphenyl ether increases and the yield of aromatic ring hydrogenation product oxydicyclohexane decreases significantly, and this catalyst effectively inhibits the direct hydrogenation of the aromatic ring of diphenyl ether and promotes the cleavage reaction of the C-O bond. This method effectively optimizes the activity of Ru / AC catalyst for the cleavage of the C-O bond of diphenyl ether and can significantly control the conversion of diphenyl ether into monocyclic target products.

[0059] Finally, the C-O bond hydrogenolysis conversion reactions of different substrates were carried out with the optimal catalyst Ru-SO / 10Zr-AC, and the results are shown in Table 3. Under the corresponding reaction conditions, diphenyl ether, benzyl phenyl ether, p-xylene ether, 4-phenoxyphenol and dibenzyl ether can be effectively converted, wherein the conversion rates are all 100%, and the products are mainly monocyclic products with C-O bond cleavage. The Ru-SO / 10Zr-AC solid superacid catalyst can effectively control the direct cleavage of the C-O bond of the aromatic ether and inhibit the hydrogenation of the aromatic ring.

[0060] Table 3 Hydrogenolysis conversion results of different substrates on Ru-SO / 10Zr-AC catalyst

[0061]

[0062] a Reaction conditions: 0.1 g of substrate, 30 mg of Ru-SO / 10Zr-AC, 20 mL of n-hexane, 1 MPa of H2. b The product yield is more than 100% because the C-O bond in the reactant is completely cleaved, and 1 mole of the bicyclic reactant is converted into 2 moles of monocyclic product.

[0063] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any modification, equivalent replacement and improvement made by those skilled in the art within the technical range disclosed by the present application, as long as it is within the spirit and principle of the present application, should be covered within the protection scope of the present application.

Claims

1. The use of activated carbon supported solid superacid catalyst in the hydrogenolysis of aromatic ether C-O bond, characterized in that, The activated carbon supported solid superacid catalyst is prepared by the following steps: (1) preparing a zirconium oxide precursor aqueous solution, then adding activated carbon powder, and after ultrasonic stirring for 5-10 min, the mixture is immersed at room temperature for 10-12 h; (2) after the immersion is completed, under stirring, ammonia water is added to adjust the pH value of the solution to 9-10, so that a precipitate is generated, and the mixture is aged at room temperature for 10-12 h; (3) suction filtration, washing the precipitate with water until no Cl- is present, and drying to obtain a solid powder containing amorphous Zr(OH)4; (4) the solid powder containing amorphous Zr(OH)4 is placed into a 1 mol / L ammonium persulfate solution, stirring for 2 h first, then immersing at room temperature for 6 h, after the immersion is completed, filtering, and drying; (5) The sample dried in step (4) was put into a tube furnace and calcined at 550 °C for 3 h under argon atmosphere. o C calcined for 3 h, and the obtained solid was labeled as SO / Zr-AC; (6) preparing a ruthenium precursor aqueous solution, after stirring for 5-15 min, adding the SO / Zr-AC obtained in step (5), and ultrasonic stirring for 15-30 min; the mixture is immersed in a vacuum drying box for 24 h, and after the immersion is completed, the mixture is dried; wherein the ruthenium loading amount is 5 wt.%; (7) The sample dried in step (6) was put into a tube furnace and reduced under argon atmosphere at 300 o C for 2 h, and then reduced under hydrogen at 300 o C for 2 h at the same flow rate; after calcination and reduction, argon was switched to cool to room temperature to obtain the activated carbon supported solid superacid catalyst Ru-SO / Zr-AC catalyst.

2. Use according to claim 1, characterized in that, In step (1), the zirconium oxide precursor is zirconium oxychloride octahydrate, and in step (6), the ruthenium precursor is ruthenium trichloride.

3. Use according to claim 1, characterized in that, In step (2), the amount of zirconium oxide in the zirconium oxide precursor accounts for 5-20% of the amount of the Zr-AC carrier.

4. Use according to claim 1, characterized in that, The temperature of drying in steps (3), (4), (6) is 110 o C, and the drying time is 12 h.

5. The use according to claim 1, characterized in that, In step (5), the argon flow rate is 200 mL / min; and in step (7), the argon flow rate is 70 mL / min.

6. The use according to claim 1, characterized in that, The temperature ramp rate in step (5) is 10 o C / min, and the temperature ramp rate in step (7) is 15 o C / min.

7. The use according to claim 1, characterized in that, The steps of the specific application include: placing the reaction substrate aryl ether, catalyst and n-hexane into a reactor, sealing and replacing three times of air with hydrogen; then, pressurizing the reactor to 1 MPa with hydrogen at room temperature; then, increasing the temperature to 180-240 o C and stirring vigorously for 1-4 h; after the experiment, naturally cooling the reaction system to room temperature and releasing the pressure; filtering the reaction mixture to remove the catalyst and analyzing the obtained organic phase after filtration by GC-MS and gas chromatography.

8. Use according to claim 7, characterized in that, The mass ratio of the catalyst to the substrate is 30%.

9. Use according to claim 7, characterized in that, The substrate aromatic ether is any one of diphenyl ether, benzyl phenyl ether, p-dimethylphenyl ether, 4-phenoxyphenol, and dibenzyl ether.

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