Catalyst for preparing phenol through catalytic hydrogenation of guaiacol as well as preparation method and application of catalyst

Abstract

The invention provides a catalyst for preparing phenol through catalytic hydrogenation of guaiacol as well as a preparation method and application of the catalyst. The preparation method of the catalyst comprises the following steps: fully dissolving magnesium nitrate, P123 and urea in deionized water, carrying out hydrothermal reaction, filtering, washing, drying and roasting to obtain an MgO carrier; immersing the MgO carrier in an alkali metal nitrate aqueous solution, drying and roasting to obtain an alkali metal element loaded MgO carrier; the alkali metal is selected from one of Li, Na, K or Cs; and immersing the alkali metal element loaded MgO carrier in a methanol solution of chloroplatinic acid, removing methanol, drying, and then carrying out reduction treatment to obtain the catalyst. The catalyst disclosed by the invention is applied to catalytic hydrodeoxygenation of guaiacol and shows excellent catalytic performance, the hydrodeoxygenation reaction conditions are mild, and the target product phenol can be obtained with high selectivity and high yield.

Description

Technical Field

[0001] The invention belongs to the technical field of phenol preparation, and particularly relates to a catalyst for preparing phenol by catalytic hydrogenation of guaiacol, and a preparation method and application thereof. Background Art

[0002] With the rapid development of social economy, fossil fuels are becoming increasingly depleted, environmental problems are becoming more and more serious, and human production and life are seriously threatened. Seeking efficient and clean new energy is an inevitable requirement for the sustainable development of human society. As the only renewable resource that can provide an organic carbon source, the development and utilization of biomass resources has attracted much attention. As a new type of renewable and clean energy, biomass energy is similar to fossil fuels in composition, mainly composed of C, H, O and other elements. It is expected to become a substitute for traditional fossil fuels and provide humans with a continuous supply of hydrocarbon resources. Among them, lignin accounts for 30-40% of the mass of biomass and is an abundant renewable raw material. In recent years, the chemical conversion reaction of lignin biomass energy has attracted extensive attention from scholars at home and abroad.

[0003] Guaiacol (Guaiacol, referred to as GUA) is the most typical model compound of lignin. Its chemical structure contains hydroxyl and methoxyl groups, and these two functional groups are widely present in lignin polymers, so the majority of researchers usually choose it for hydrodeoxygenation reaction research. Under the action of a catalyst, guaiacol can obtain phenol (Phenol) through hydrodeoxygenation reaction. Phenol is a very important bulk chemical raw material and intermediate in the chemical industry, and is crucial in fine chemicals and oil refining industries, such as: it can be used to synthesize phenolic resins to manufacture high temperature resistant and corrosion resistant materials; synthesize caprolactam for the production of artificial synthetic fibers and artificial leather; synthesize acetylsalicylic acid to prepare aspirin for the pharmaceutical industry; therefore, phenol is widely used. At present, phenol is mainly synthesized by isopropylbenzene process, which consumes a large amount of petroleum-derived benzene, so it is very meaningful to use renewable biomass instead of petroleum as raw material to produce phenol, and it is of great significance to selectively hydrodeoxygenate guaiacol to produce bio-based phenol.

[0004] At present, the catalysts used in the hydrodeoxygenation reaction of guaiacol mainly include precious metal catalysts and non-precious metal catalysts. Patent document CN 115894177 A uses a ruthenium-containing catalyst to catalyze the hydrodeoxygenation reaction of guaiacol. When using Ru / α-MoC catalyst, under the conditions of 300°C and 3MPa hydrogen pressure, the conversion rate of guaiacol can reach 88%, but the yield of phenol products is only 17%, and the yield of hydrocarbon products is 44%. Higher reaction temperature and hydrogen partial pressure will increase the possibility of benzene ring saturation reaction, so that phenol is further hydrogenated to generate cyclohexanol and cyclohexane, reducing phenol selectivity. Patent document CN105622355 A uses a gold-containing catalyst to hydrodeoxygenate guaiacol. It is found that guaiacol reacts for 4h at 300°C and 3MPa hydrogen pressure under the catalytic action of Au / TiO2 catalyst, and its conversion rate reaches 53%, and the yield of phenol reaches 48%. "Bui VN, Laurenti D, Afanasiev P, et al. Hydrodeoxygenation of guaiacol with comocatalysts. part Ⅰ: Promoting effect of cobalt on HDO selectivity and activity [J]. Applied Catalysis B: Environmental, 2011, 101: 239-245" studied the performance of CoMoS / Al2O3 catalyst in the hydrogenation reaction of guaiacol. When the reaction temperature was 300°C, the main products were phenol, cresol, benzene ring saturated products and catechol, with yields of 32%, 26%, 13% and 10%, respectively. From the above, it can be found that if traditional non-precious metal hydrogenation catalysts such as Co and Mo are used, the distribution of products is mostly dispersed, usually including phenol compounds, benzene derivatives and benzene ring saturated products; at the same time, the reaction conditions are harsh (high temperature and high pressure), and the reaction rate is low, so the reaction effect is not ideal. Precious metal catalysts have excellent adsorption capacity for reactants and active hydrogen produced during hydrogenation, and show good hydrodeoxygenation activity in the catalytic hydrogenolysis of guaiacol, so they have better catalytic performance than other catalysts. However, during the hydrogenolysis reaction, compounds containing benzene rings are prone to hydrogenation side reactions under the action of precious metals, reducing the selectivity of the target product and thus reducing the yield of the target product. Therefore, improving the selectivity of precious metal catalysts for phenol, thereby catalyzing hydrodeoxygenation to prepare phenol with high yield, is one of the current research focuses. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a catalyst for preparing phenol by catalytic hydrogenation of guaiacol, and a preparation method and application thereof. The catalyst of the present invention is an alkali metal-modified Pt / MgO catalyst; it is applied to catalyze the hydrodeoxygenation of guaiacol and exhibits excellent catalytic performance, the hydrodeoxygenation reaction conditions are mild, and the target product phenol can be obtained with high selectivity and high yield.

[0006] The technical solution of the present invention is as follows:

[0007] A catalyst for preparing phenol by catalytic hydrogenation of guaiacol, wherein the catalyst is a MgO carrier loaded with a Pt element and an alkali metal element, wherein the alkali metal is selected from one of Li, Na, K or Cs.

[0008] The method for preparing the catalyst for preparing phenol by catalytic hydrogenation of guaiacol comprises the steps of:

[0009] (1) fully dissolving magnesium nitrate, P123 and urea in deionized water, subjecting them to a hydrothermal reaction, and then filtering, washing, drying and calcining to obtain a MgO carrier;

[0010] (2) immersing the MgO carrier in an aqueous solution of an alkali metal nitrate, drying and calcining to obtain a MgO carrier loaded with an alkali metal element; the alkali metal is selected from one of Li, Na, K or Cs;

[0011] (3) The MgO carrier loaded with alkali metal elements is immersed in a methanol solution of chloroplatinic acid, the methanol is removed, the solution is dried, and then subjected to reduction treatment to obtain a catalyst for catalytic hydrogenation of guaiacol to prepare phenol.

[0012] Preferably according to the present invention, in step (1), the molar ratio of urea to magnesium nitrate is 2-10:1, preferably 5-10:1, most preferably 10:1; the mass ratio of magnesium nitrate to P123 is 0.3-0.7:1.

[0013] Preferably according to the present invention, in step (1), the volume ratio of the molar amount of magnesium nitrate to deionized water is 0.2-0.8 mol / L.

[0014] Preferably, according to the present invention, in step (1), the hydrothermal reaction temperature is 80-160° C., and the hydrothermal reaction time is 12-24 h.

[0015] Preferably, according to the present invention, in step (1), the calcination temperature is 500°C-900°C, the calcination time is 2-4h, and the calcination atmosphere is a mixed atmosphere of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

[0016] According to the preferred embodiment of the present invention, in step (2), the alkali metal is Li or Na, preferably Na.

[0017] Preferably according to the present invention, in step (2), the concentration of the alkali metal nitrate aqueous solution is 0.1-1.2 mol / L, preferably 0.3-0.6 mol / L, and more preferably 0.572 mol / L.

[0018] Preferably according to the present invention, in step (2), the volume ratio of the mass of the MgO carrier to the aqueous solution of the alkali metal nitrate is 0.125-0.25 g / mL, preferably 0.25 g / mL.

[0019] Preferably according to the present invention, in step (2), the immersion temperature is room temperature and the immersion time is 6-10 hours.

[0020] Preferably, according to the present invention, in step (2), the calcination temperature is 400-600°C, the calcination time is 2-4h, and the calcination atmosphere is a mixed atmosphere of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

[0021] Preferably according to the present invention, in step (3), the concentration of the methanol solution of chloroplatinic acid is 0.01-1 mmol / L, preferably 0.55 mmol / L.

[0022] Preferably, according to the present invention, in step (3), the volume ratio of the mass of the MgO carrier loaded with alkali metal elements to the methanol solution of chloroplatinic acid is 1.0-2.0 g:60-70 mL, preferably 1.0 g:70 mL.

[0023] Preferably, according to the present invention, in step (3), the immersion conditions are: stirring at room temperature for 6-10 hours.

[0024] Preferably according to the present invention, in step (3), methanol is removed by rotary evaporation at 40° C., the drying temperature is 60-100° C., and the drying time is 10-20 h.

[0025] Preferably, according to the present invention, in step (3), the reduction treatment temperature is 300-400° C., the reduction treatment time is 1-3 h, and the reduction treatment atmosphere is hydrogen.

[0026] Application of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol.

[0027] According to a preferred embodiment of the present invention, the application method is as follows: in a n-decane solvent, under the action of the above catalyst, guaiacol reacts with H2 to obtain phenol.

[0028] Preferably, the mass ratio of guaiacol to the volume ratio of n-decane solvent is 10-20 g / L.

[0029] Preferably, the mass ratio of the catalyst to guaiacol is 0.1-0.5:1.

[0030] Preferably, the reaction temperature is 240-320° C., preferably 280-300° C., the hydrogen pressure is 0.1-1 MPa, the reaction time is 2-8 h, preferably 4-8 h, and the reaction is carried out under stirring conditions.

[0031] According to the present invention, the reaction solution obtained by the reaction is purified according to the existing method to obtain phenol.

[0032] The technical features and beneficial effects of the present invention are as follows:

[0033] (1) The present invention selects MgO as a catalyst carrier. The alkaline carrier MgO can inhibit the hydrogenation reaction of the benzene ring, improve the selectivity of phenol, and reduce the formation of carbon deposits during the reaction, thereby extending the life of the catalyst. By controlling the synthesis conditions of the catalyst carrier MgO, the alkaline sites and the number of surface defects on the MgO surface are regulated, thereby affecting the adsorption and desorption behavior of guaiacol and phenol, thereby improving the catalytic reaction performance of guaiacol hydrodeoxygenation. The surface acidity and alkalinity of the catalyst are further regulated by modifying Pt / MgO with alkali metals, thereby achieving high reaction selectivity and high yield preparation of phenol.

[0034] (2) The hydrodeoxygenation reaction conditions of guaiacol in the present invention are relatively mild. The use of a lower hydrogen partial pressure can inhibit the hydrogenation reaction of the benzene ring, which is beneficial to the production of aromatic compounds such as phenol, thereby improving the selectivity and yield of phenol. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a scanning electron microscope image of the MgO support prepared in Example 2. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

[0037] Unless otherwise specified, the reagents and equipment used in the examples are all from the prior art.

[0038] In Example 1-4, the molar ratio of urea to magnesium in the preparation process of the catalyst carrier MgO was changed to adjust the basic sites and the number of surface defects on the surface of the catalyst carrier MgO, and to study its influence on the catalytic performance of the Pt / MgO catalyst.

[0039] Example 1

[0040] A method for preparing a Pt / MgO catalyst comprises the following steps:

[0041] (1) Preparation of MgO carrier: MgO was synthesized by hydrothermal method. First, 25 mmol of magnesium nitrate was dissolved in 50 ml of deionized water, and then 7.25 g of P123 (Mn is about 5800, available from MacLean Reagent Company) was added and dispersed evenly by ultrasonication. Urea was then added to make the molar ratio of urea to magnesium nitrate 2:1, and the mixture was fully mixed and dispersed evenly. The mixture was then hydrothermalized in an oven at 120°C for 24 h, filtered and washed to obtain a precipitate, dried, and then calcined at 500°C for 4 h in an O2 / Ar (20 / 40 mL / min) atmosphere to obtain a MgO carrier.

[0042] (2) Pt / MgO catalyst was prepared by impregnation method. The specific preparation process was as follows: 0.02g (0.0386mmol) H2PtCl6·6H2O was dissolved in 70mL methanol, and then 1.0g MgO carrier was slowly added to the above metal salt solution. The resulting suspension was stirred at room temperature for 8h. Then, the methanol was removed by rotary evaporator at 40°C, and the obtained solid powder was dried in an oven at 80°C for 12h. Finally, the prepared catalyst was reduced to 400°C in hydrogen (40mL / min) at a rate of 10°C / min for 2h. The theoretical metal loading of Pt / MgO catalyst is 0.8wt.%.

[0043] The application of the above-mentioned Pt / MgO catalyst in the preparation of phenol adopts an intermittent reaction, and the specific steps are:

[0044] (1) Take a mechanically stirred autoclave, add 440 mg of guaiacol, 30 ml of n-decane, 220 mg of internal standard dodecane (used as an internal reference standard for quantitative analysis), and 150 mg of catalyst, tighten the autoclave and check the air tightness of the device. After ensuring that the device is leak-proof, introduce 0.1 MPa of H2, stir at 800 rpm, set the temperature to 280°C, and react for 4 h.

[0045] (2) After the reaction is completed, the liquid product is collected and analyzed by gas chromatography. The catalyst is recovered by centrifugation.

[0046] The reaction results showed that the conversion rate of guaiacol was 44.3% and the selectivity of phenol was 78.4%.

[0047] Wherein: Conversion rate of guaiacol = (amount of guaiacol substance at the beginning of the reaction - amount of guaiacol substance at the end of the reaction) / amount of guaiacol substance at the beginning of the reaction × 100%

[0048] Yield of phenol = amount of phenol at the end of the reaction / amount of guaiacol at the start of the reaction × 100%

[0049] Selectivity of phenol = yield of phenol / conversion rate of guaiacol × 100%

[0050] Example 2

[0051] A method for preparing a Pt / MgO catalyst is as described in Example 1, except that in step (1) the MgO carrier preparation method, the molar ratio of urea to magnesium nitrate is 5:1; the other steps and conditions are the same as in Example 1.

[0052] The specific method for using the above Pt / MgO catalyst in preparing phenol is the same as that in Example 1.

[0053] The reaction results showed that the conversion rate of guaiacol was 53.5% and the selectivity of phenol was 80.2%.

[0054] The scanning electron microscope image of the MgO carrier prepared in this example is as follows Figure 1 As shown, its microscopic morphology is granular and flaky.

[0055] Example 3

[0056] A method for preparing a Pt / MgO catalyst is as described in Example 1, except that in step (1) the MgO carrier preparation method, the molar ratio of urea to magnesium nitrate is 10:1; the other steps and conditions are the same as in Example 1.

[0057] The specific method for using the above Pt / MgO catalyst in preparing phenol is the same as that in Example 1.

[0058] The reaction results showed that the conversion rate of guaiacol was 62.2% and the selectivity of phenol was 85.4%.

[0059] Example 4

[0060] A method for preparing a Pt / MgO catalyst is as described in Example 1, except that in step (1) the MgO carrier preparation method, the molar ratio of urea to magnesium nitrate is 15:1; the other steps and conditions are the same as in Example 1.

[0061] The specific method for using the above Pt / MgO catalyst in preparing phenol is the same as that in Example 1.

[0062] The reaction results showed that the conversion rate of guaiacol was 40.3% and the selectivity of phenol was 71.7%.

[0063] The reaction results of Comparative Examples 1-4 are shown in Table 1.

[0064] Table 1 Test results

[0065]

[0066] From the reaction results of comparative examples 1-4 in Table 1, it can be seen that, as the molar ratio of urea to magnesium increases during the preparation of the catalyst carrier MgO, the conversion rate of guaiacol increases continuously, and the yield of phenol also increases continuously. However, when the molar ratio of urea to magnesium increases to 15:1, the conversion rate of guaiacol begins to decrease, and the yield of phenol also decreases. It can be seen from this that the MgO synthesized with a molar ratio of urea to magnesium of 10:1, the Pt / MgO catalyst has good catalytic activity, and the conversion rate of guaiacol can reach 62.2%. This may be attributed to the large number of basic sites and surface defects on the surface of MgO synthesized with a molar ratio of urea to magnesium of 10:1. A large number of basic sites on the surface of MgO may strongly bind to the hydrogen atoms of the acidic phenolic hydroxyl groups in guaiacol at the metal carrier interface, which may be conducive to the preferential adsorption of guaiacol, thereby indirectly activating C aryl -OCH3 bond, thereby accelerating the formation of phenol from guaiacol HDO.

[0067] Example 3, Example 5-8 are catalytic hydrogenation reactions of guaiacol under different reaction pressures

[0068] Embodiment 5-8

[0069] A method for preparing a Pt / MgO catalyst is the same as that in Example 3.

[0070] The application of the above Pt / MgO catalyst in the preparation of phenol is as described in Example 3, except that the reaction pressures are 0.2, 0.3, 0.4, and 0.5 MPa, respectively.

[0071] The reaction results are shown in Table 2

[0072] Table 2 Results of different reaction pressures

[0073]

[0074] As can be seen from the reaction results of Example 3 and Example 5-8, when the H2 pressure is 0.1MPa, it has good catalytic activity and the phenol selectivity can reach 85.4%. As the H2 pressure increases, the conversion rate of guaiacol decreases and the yield of phenol decreases. Continuing to increase the pressure will further hydrogenate phenol into cyclohexanol and cyclohexanone. The H2 pressure of 0.1MPa is conducive to the catalytic guaiacol of Pt / MgO catalyst to generate phenol in a directional manner. Therefore, the hydrogen pressure of the reaction is selected to be 0.1MPa.

[0075] Examples 9-12 Pt / MgO catalysts modified with different alkali metals (Li, Na, K, Cs) for hydrodeoxygenation of guaiacol

[0076] Examples 9-12

[0077] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol comprises the following steps:

[0078] (1) Preparation of MgO carrier: MgO was synthesized by hydrothermal method. First, 25 mmol of magnesium nitrate was dissolved in 50 ml of deionized water, and then 7.25 g of P123 (Mn is about 5800, available from MacLean Reagent Company) was added and dispersed evenly by ultrasonication. Urea was then added to make the molar ratio of urea to magnesium nitrate 10:1, and the mixture was fully mixed and dispersed evenly. The mixture was then hydrothermaled in an oven at 120°C for 24 h, filtered and washed to obtain a precipitate, dried, and then calcined at 500°C for 4 h in an O2 / Ar (20 / 40 mL / min) atmosphere to obtain a MgO carrier.

[0079] (2) Modification of the carrier MgO with different alkali metals (Li, Na, K, Cs) was carried out by impregnation method. 1 g of MgO carrier was immersed in 4 mL of 0.572 mol / L alkali metal nitrate aqueous solution at room temperature for 8 h. The carrier was dried and calcined at 500 °C in an O2 / Ar (20 / 40 mL / min) atmosphere for 4 h to obtain a MgO carrier loaded with alkali metal elements; this was defined as M / MgO (M = Li, Na, K or Cs).

[0080] (3) Pt-M / MgO (M = Li, Na, K or Cs) catalyst was prepared by impregnation method. The specific preparation process is as follows: 0.02g H2PtCl6·6H2O was dissolved in 70mL methanol, and then 1.0g M / MgO was slowly added to the above metal salt solution. The resulting suspension was stirred at room temperature for 8h. Then, the methanol was removed by rotary evaporator at 40°C, and the obtained solid powder was dried in an oven at 80°C for 12h. Finally, the prepared catalyst was reduced to 400°C in hydrogen (40mL / min) at a rate of 10°C / min for 2h.

[0081] The application of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in preparing phenol adopts an intermittent reaction, and the specific steps are:

[0082] (1) Take a mechanically stirred high-pressure reactor, add 440 mg of guaiacol, 30 ml of n-decane, 220 mg of internal standard dodecane, and 150 mg of catalyst, tighten the reactor and check the air tightness of the device. After ensuring that the device is leak-proof, introduce 0.1 MPa H2, stir at 800 rpm, set the temperature to 280°C, and react for 4 h.

[0083] (2) After the reaction is completed, the liquid product is collected and analyzed by gas chromatography. The catalyst is recovered by centrifugation.

[0084] The reaction results are shown in Table 3.

[0085] Table 3 Reaction results of different alkali metal (Li, Na, K, Cs) modified catalysts

[0086]

[0087] It can be seen from Examples 3 and 9-12 that the addition of alkali metal additives Na and Li improves the catalyst activity, especially after the addition of Na modification, the guaiacol conversion rate is increased to 87.8%, and the phenol selectivity can reach 90.7%. This may be because after the alkali metal Na modification, the number and strength of the basic sites on the surface of the Pt / MgO catalyst change, and the phenol yield is improved.

[0088] Examples 13-16 Catalysts with different sodium modification amounts are used for the hydrodeoxygenation reaction of guaiacol

[0089] Examples 13-16

[0090] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol comprises the following steps:

[0091] Step (1) is the same as step (1) of Example 10.

[0092] Step (2) is as described in step (2) of Example 10, except that the concentrations of the sodium nitrate aqueous solution are 0.11 mol / L, 0.336 mol / L, 0.76 mol / L, and 1.087 mol / L, respectively.

[0093] Step (3) is the same as step (3) of Example 10. The catalyst obtained is defined as Pt-nNa / MgO (n=1, 3, 7, 10). The catalyst obtained in Example 10 is defined as Pt-5Na / MgO.

[0094] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol is the same as in Example 10.

[0095] The reaction results are shown in Table 4.

[0096] Table 4 Reaction results of catalysts with different sodium modification amounts

[0097]

[0098] As can be seen from Examples 13-16, after modification with alkali metal sodium, the catalytic activity is significantly improved. With the increase of the amount of sodium modification, the guaiacol conversion rate and the phenol yield both show a trend of first increasing and then decreasing. When the amount of sodium modification is 5wt.%, it has a higher catalytic activity, the guaiacol conversion rate is increased to 87.8%, and the phenol selectivity can reach 90.7%. This may be because after modification with alkali metal Na, the alkalinity of the carrier increases, which is conducive to the formation of phenol.

[0099] Example 10 and Examples 17-21 Catalytic Hydrogenation of Guaiacol at Different Reaction Temperatures

[0100] Examples 17-21

[0101] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol, same as Example 10.

[0102] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in preparing phenol is as described in Example 10, except that the reaction temperatures are 240, 260, 270, 290, and 300° C., respectively.

[0103] The reaction results are shown in Table 5.

[0104] Table 5 Results of different reaction temperatures

[0105]

[0106] It can be seen from Table 6 that as the reaction temperature increases, the reaction activity increases and the phenol yield increases. The results show that high temperature promotes the cleavage of the CO bond, thereby promoting the formation of phenol.

[0107] Examples 22-24 Catalytic hydrogenation of guaiacol at different reaction times

[0108] Examples 22-24

[0109] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol, same as Example 21.

[0110] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol is as described in Example 21, except that the reaction times are 2 h, 6 h, and 8 h, respectively.

[0111] The reaction results are shown in Table 6.

[0112] Table 6 Results of different reaction times

[0113]

[0114] It can be seen from Examples 22-24 that when the reaction is carried out under the conditions of 300° C. and 0.1 MPa H2, the conversion rate of guaiacol and the yield of phenol are improved by prolonging the reaction time. When the reaction time is 6 h, the conversion rate of guaiacol can reach 95% and the yield of phenol is 87.2%. However, when the reaction time is extended to 8 h, the selectivity of phenol decreases, indicating that as the reaction time is extended, phenol will continue to react and further hydrogenate to form cyclohexanone and cyclohexanol. Therefore, it is necessary to properly control the reaction time to improve the yield of phenol.

[0115] Comparative Examples 1 and 2: Changing the type of magnesium salt added during the hydrothermal synthesis of magnesium oxide, and loading platinum to catalyze the hydrodeoxygenation reaction of guaiacol

[0116] Comparative Example 1-2

[0117] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol is as described in Example 23, except that in step (1) of the MgO carrier preparation method, the magnesium salts added are magnesium chloride and magnesium acetate, respectively, and the other steps and conditions are the same as those in Example 23.

[0118] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol is the same as in Example 23.

[0119] The reaction results of Comparative Example 1 showed that the conversion rate of guaiacol was 80.2% and the selectivity of phenol was 82.3%.

[0120] The reaction results of Comparative Example 2 showed that the guaiacol conversion rate was 76.4% and the phenol selectivity was 81.8%.

[0121] Comparing Example 23 with Comparative Example 1, it can be seen from Comparative Example 2 that when the magnesium salt added in the hydrothermal synthesis of magnesium oxide is magnesium nitrate, the catalyst has a higher catalytic activity. This may be because the use of magnesium nitrate helps to form uniformly distributed grains and avoid agglomeration, thereby obtaining a magnesium oxide carrier with good dispersibility, having a higher specific surface area, and being able to provide more active sites, which is conducive to the adsorption and catalytic reaction.

[0122] Comparative Example 3: Chemical precipitation method to synthesize magnesium oxide support, loaded with platinum to catalyze guaiacol hydrodeoxygenation reaction

[0123] Comparative Example 3

[0124] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol, as described in Example 23, except that: the preparation step of the MgO carrier in step (1) is as follows: MgO is synthesized by a method of magnesium acetate and oxalic acid precipitation, and the specific steps are as follows: First, 8g of magnesium acetate is dissolved in 50mL of deionized water at room temperature, and the obtained solution is added to 200mL of an aqueous solution containing 5g of oxalic acid. Finally, the mixed solution is stirred at room temperature for 12h, and the formed magnesium oxalate precipitate is washed three times with deionized water and ethanol respectively, and the product is placed in a 100°C oven and dried overnight. The obtained white powder is heated to 500°C at a rate of 5°C / min under an O2 / Ar (20 / 40mL / min) atmosphere, and the temperature is kept constant for 4h to obtain a magnesium oxide carrier. The other steps and conditions are the same as in Example 23.

[0125] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol is the same as in Example 23.

[0126] The reaction results showed that the conversion rate of guaiacol was 72.6% and the selectivity of phenol was 80.2%.

[0127] Comparison of Example 23 and Comparative Example 3 shows that the hydrothermally synthesized magnesium oxide, Pt-5Na / MgO catalyst has a higher catalytic activity. This may be attributed to the fact that the magnesium oxide particles prepared by the hydrothermal method have a regular morphology and a large specific surface area, which can provide more active sites, making it easier for reactant molecules to adsorb on the catalyst surface, thereby increasing the contact area between the reactant and the catalyst, increasing the rate of the catalytic reaction, and accelerating the catalytic hydrogenation of guaiacol to produce phenol.

[0128] Comparative Example 4, the order of catalyst preparation steps was changed to study the effect of metal impregnation order on catalytic performance.

[0129] Comparative Example 4

[0130] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol comprises the following steps:

[0131] (1) The preparation of MgO carrier is the same as step (1) of Example 23.

[0132] (2) Pt / MgO was prepared by impregnation method. The specific preparation process is as follows: 0.02g H2PtCl6·6H2O was dissolved in 70mL methanol, and then 1.0g MgO was slowly added to the above metal salt solution. The resulting suspension was stirred at room temperature for 8h. The methanol was then removed by rotary evaporator at 40°C, and the obtained solid powder was dried in an oven at 80°C for 12h. Then, the MgO carrier loaded with platinum was calcined at 500°C in a tube furnace in an O2 / Ar (20 / 40mL / min) atmosphere for 4h.

[0133] (3) The Pt-5Na / MgO catalyst was prepared by the impregnation method. 1 g of the Pt / MgO carrier was immersed in 4 mL of a 0.572 mol / L sodium nitrate aqueous solution at room temperature for 8 h, dried, and reduced in hydrogen (40 mL / min) at a rate of 10°C / min to 400°C for 2 h to obtain the Pt-5Na / MgO catalyst.

[0134] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol is the same as in Example 23.

[0135] The reaction results showed that the conversion rate of guaiacol was 70.2% and the selectivity of phenol was 81.4%.

[0136] It can be seen from Example 23 and Comparative Example 4 that different orders of impregnating metals during the catalyst preparation process will affect the catalytic performance. The catalytic performance of the catalyst obtained by first modifying the magnesium oxide carrier with alkali metal sodium and then impregnating platinum is better than the catalytic performance of the catalyst first impregnated with platinum and then impregnated with alkali metal sodium. This may be because the acidity and alkalinity of the catalyst surface are changed by impregnating alkali metal sodium first, and the electronic structure of platinum changes, thereby affecting the catalytic performance of the catalyst. The impregnation order may also affect the dispersion of the metal on the carrier, and uniformly dispersed metal particles generally have higher catalytic activity. Impregnating alkali metal sodium first will adjust the dispersion of platinum and promote the uniform distribution of platinum on the carrier, so it has higher catalytic activity.

[0137] Comparative Example 5: Hydrodeoxygenation of guaiacol catalyzed by magnesium oxide supported alkali metal sodium

[0138] Comparative Example 5

[0139] A method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol comprises the following steps:

[0140] (1) The preparation of MgO carrier is the same as step (1) of Example 23.

[0141] (2) The Na / MgO catalyst was prepared by the impregnation method. 1 g of MgO carrier was immersed in 4 mL of 0.572 mol / L sodium nitrate aqueous solution at room temperature for 8 h. The catalyst was then dried and calcined at 500 °C in an O2 / Ar (20 / 40 mL / min) atmosphere for 4 h to obtain a MgO carrier loaded with alkali metal elements.

[0142] The use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol in the preparation of phenol is the same as in Example 23.

[0143] The reaction results showed that the conversion rate of guaiacol was 12.8% and the selectivity of phenol was 17.2%.

[0144] As can be seen from Comparative Example 5, MgO only loaded with alkali metal sodium has very low catalytic activity for guaiacol hydrogenation, and guaiacol is substantially not converted. The phenol selectivity is only 17.2%, so it is difficult to achieve a high yield of phenol by only loading alkali metal sodium.

[0145] The above embodiments are the implementation methods adopted by the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts created by the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A catalyst for preparing phenol by catalytic hydrogenation of guaiacol, characterized in that: The catalyst is a MgO carrier loaded with Pt element and alkali metal element, wherein the alkali metal is selected from one of Li, Na, K or Cs.

2. The method for preparing the catalyst for preparing phenol by catalytic hydrogenation of guaiacol as claimed in claim 1, comprising the steps of: (1) fully dissolving magnesium nitrate, P123 and urea in deionized water, subjecting them to a hydrothermal reaction, and then filtering, washing, drying and calcining to obtain a MgO carrier; (2) immersing the MgO carrier in an aqueous solution of an alkali metal nitrate, drying and calcining to obtain a MgO carrier loaded with an alkali metal element; the alkali metal is selected from one of Li, Na, K or Cs; (3) The MgO carrier loaded with alkali metal elements is immersed in a methanol solution of chloroplatinic acid, the methanol is removed, the solution is dried, and then subjected to reduction treatment to obtain a catalyst for catalytic hydrogenation of guaiacol to prepare phenol.

3. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (1), the molar ratio of urea to magnesium nitrate is 2-10:1, preferably 5-10:1, and most preferably 10:1; the mass ratio of magnesium nitrate to P123 is 0.3-0.7:

1.

4. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (1), one or more of the following conditions are included: i. The volume ratio of the molar amount of magnesium nitrate to deionized water is 0.2-0.8 mol / L; ii. The hydrothermal reaction temperature is 80-160°C and the hydrothermal reaction time is 12-24h; iii. The calcination temperature is 500°C-900°C, the calcination time is 2-4h, and the calcination atmosphere is a mixed atmosphere of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

5. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (2), the alkali metal is Li or Na, preferably Na.

6. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (2), the concentration of the alkali metal nitrate aqueous solution is 0.1-1.2 mol / L, preferably 0.3-0.6 mol / L, and more preferably 0.572 mol / L.

7. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (2), the volume ratio of the mass of the MgO carrier to the aqueous solution of alkali metal nitrate is 0.125-0.25 g / mL, preferably 0.25 g / mL.

8. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (2), one or more of the following conditions are included: i. The immersion temperature is room temperature and the immersion time is 6-10h; ii. The calcination temperature is 400-600°C, the calcination time is 2-4h, and the calcination atmosphere is a mixed atmosphere of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

9. The method for preparing a catalyst for preparing phenol by catalytic hydrogenation of guaiacol according to claim 2, characterized in that: In step (3), one or more of the following conditions are included: i. The concentration of the methanol solution of chloroplatinic acid is 0.01-1 mmol / L, preferably 0.55 mmol / L; ii. The volume ratio of the mass of the MgO carrier loaded with alkali metal elements to the methanol solution of chloroplatinic acid is 1.0-2.0 g:60-70 mL, preferably 1.0 g:70 mL; iii. Immersion conditions: stirring at room temperature for 6-10 hours; iv. Remove methanol by rotary evaporation at 40°C, with a drying temperature of 60-100°C and a drying time of 10-20h; v. The reduction treatment temperature is 300-400°C, the reduction treatment time is 1-3h, and the reduction treatment atmosphere is hydrogen.

10. Use of the catalyst for preparing phenol by catalytic hydrogenation of guaiacol as claimed in claim 1 in preparing phenol; preferably, the application method is as follows: in n-decane solvent, under the action of the above catalyst, guaiacol reacts with H2 to obtain phenol; Further preferably, the mass ratio of guaiacol to n-decane solvent is 10-20 g / L; the mass ratio of catalyst to guaiacol is 0.1-0.5:1; the reaction temperature is 240-320° C., preferably 280-300° C., the hydrogen pressure is 0.1-1 MPa, the reaction time is 2-8 h, preferably 4-8 h, and the reaction is carried out under stirring conditions.

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