A catalyst for preparing phenol by catalytic hydrogenation of guaiacol and a preparation method and application thereof

Abstract

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

Description

Technical Field

[0001] This invention belongs to the field of phenol preparation technology, specifically relating to a catalyst for the catalytic hydrogenation of guaiacol to phenol, its preparation method, and its application. Background Technology

[0002] With rapid socio-economic development, fossil fuels are becoming increasingly depleted, and environmental problems are becoming more and more serious, severely threatening human production and lives. Seeking efficient and clean new energy sources is an inevitable requirement for the sustainable development of human society. As the only renewable resource that can provide organic carbon, the development and utilization of biomass resources has attracted much attention. Biomass energy, as a new type of renewable and clean energy, has the potential to become a substitute for traditional fossil fuels due to its similar composition to fossil fuels, mainly composed of elements such as C, H, and O, providing a sustainable supply of hydrocarbon resources for humanity. Lignin accounts for 30-40% of the mass of biomass and is an abundant renewable raw material. In recent years, the chemical conversion reactions of lignin-based biomass have received widespread attention from scholars both domestically and internationally.

[0003] Guaiacol (GUA) is the most typical model compound of lignin, containing hydroxyl and methoxy groups in its chemical structure. These two functional groups are widely present in lignin polymers, making them a common choice for research on hydrodeoxygenation reactions. Under the action of a catalyst, guaiacol can be converted to phenol via hydrodeoxygenation. Phenol is a very important bulk chemical raw material and intermediate in the chemical industry, crucial in fine chemicals and oil refining. For example, it can be used to synthesize phenolic resins to manufacture high-temperature and corrosion-resistant materials; to synthesize caprolactam for the production of synthetic fibers and artificial leather; and to synthesize acetylsalicylic acid to prepare aspirin for the pharmaceutical industry. Therefore, phenol has a wide range of applications. Currently, phenol is mainly synthesized through the cumene process, which consumes a large amount of petroleum-derived benzene. Therefore, using renewable biomass instead of petroleum as a raw material for phenol production is very meaningful. The selective hydrodeoxygenation of guaiacol to produce bio-based phenol is of great significance.

[0004] Currently, the catalysts used in the hydrodeoxygenation reaction of guaiacol mainly include noble metal catalysts and non-noble metal catalysts. Patent document CN 115894177 A uses a ruthenium-containing catalyst to catalyze the hydrodeoxygenation reaction of guaiacol. When using a Ru / α-MoC catalyst, under conditions of 300℃ and 3MPa hydrogen pressure, the conversion rate of guaiacol can reach 88%, but the yield of phenolic products is only 17%, and the yield of hydrocarbon products is 44%. Higher reaction temperatures and hydrogen partial pressures increase the possibility of benzene ring saturation reactions, leading to further hydrogenation of phenol to cyclohexanol and cyclohexane, thus reducing phenol selectivity. Patent document CN105622355 A uses a gold-containing catalyst to perform the hydrodeoxygenation reaction of guaiacol. It found that under the catalysis of an Au / TiO2 catalyst, at 300℃ and 3MPa hydrogen pressure for 4 hours, the conversion rate of guaiacol reaches 53%, and the yield of phenol reaches 48%. The study investigated the performance of CoMoS / Al2O3 catalysts in the hydrogenation of guaiacol. At a reaction temperature of 300℃, the main products were phenol, cresol, benzene ring-saturated products, and catechol, with yields of 32%, 26%, 13%, and 10%, respectively. This suggests that when using traditional non-precious metal hydrogenation catalysts such as Co and Mo, the product distribution is generally dispersed, typically including phenolic compounds, benzene derivatives, and benzene ring-saturated products. Furthermore, the reaction conditions are harsh (high temperature and high pressure), resulting in a low reaction rate and ultimately unsatisfactory reaction performance. Noble metal catalysts exhibit excellent adsorption capacity for reactants and active hydrogen generated during hydrogenation, demonstrating good hydrodeoxygenation activity in the catalytic hydrogenolysis of guaiacol, thus showing better catalytic performance than other catalysts. However, during the hydrogenolysis reaction, compounds containing benzene rings are prone to undergoing hydrogenation side reactions under the influence of noble metals, reducing the selectivity of the target product and consequently decreasing its yield. Therefore, improving the selectivity of noble metal catalysts for phenol, thereby achieving high-yield catalytic hydrodeoxygenation to prepare phenol, is currently one of the key research focuses. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a catalyst for the catalytic hydrogenation of guaiacol to phenol, its preparation method, and its application. The catalyst of this invention is an alkali metal-modified Pt / MgO catalyst; it exhibits excellent catalytic performance in the catalytic hydrogenation and deoxygenation of guaiacol, with mild reaction conditions, and can obtain the target product phenol with high selectivity and high yield.

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

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

[0008] The above-mentioned method for preparing the catalyst for the catalytic hydrogenation of guaiacol to phenol includes the following steps:

[0009] (1) Magnesium nitrate, P123 and urea are fully dissolved in deionized water, and after hydrothermal reaction, MgO carrier is obtained by filtration, washing, drying and calcination.

[0010] (2) The MgO support is immersed in an aqueous solution of alkali metal nitrate, and then dried and calcined to obtain the MgO support loaded with alkali metal elements; the alkali metal is selected from Li, Na, K or Cs.

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

[0012] According to a preferred embodiment of the present invention, 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.

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

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

[0015] According to a preferred embodiment of the present invention, in step (1), the calcination temperature is 500℃-900℃, the calcination time is 2-4h, and the calcination atmosphere is a mixture of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

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

[0017] According to a preferred embodiment of 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] According to a preferred embodiment of the present invention, in step (2), the mass ratio of the MgO support to the volume ratio of the alkali metal nitrate aqueous solution is 0.125-0.25 g / mL, preferably 0.25 g / mL.

[0019] According to a preferred embodiment of the present invention, in step (2), the immersion temperature is room temperature and the immersion time is 6-10 hours.

[0020] According to a preferred embodiment of the present invention, in step (2), the calcination temperature is 400-600℃, the calcination time is 2-4h, and the calcination atmosphere is a mixture of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

[0021] According to a preferred embodiment of 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] According to a preferred embodiment of the present invention, in step (3), the mass ratio of the MgO support loaded with alkali metal elements to the volume ratio of the methanol solution of chloroplatinic acid is 1.0-2.0 g: 60-70 mL, preferably 1.0 g: 70 mL.

[0023] According to a preferred embodiment of the present invention, in step (3), the immersion conditions are: stirring at room temperature for 6-10 hours.

[0024] According to a preferred embodiment of 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 10-20h.

[0025] According to a preferred embodiment of the present invention, in step (3), the reduction treatment temperature is 300-400℃, the reduction treatment time is 1-3h, and the reduction treatment atmosphere is hydrogen.

[0026] The above-mentioned catalyst for the catalytic hydrogenation of guaiacol to phenol is applied in the preparation of phenol.

[0027] According to a preferred embodiment of the present invention, the application method is as follows: guaiacol reacts with H2 in n-decane solvent under the action of the above catalyst 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 catalyst to guaiacol is 0.1-0.5:1.

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

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

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

[0033] (1) In this invention, MgO is selected as the catalyst support. The basic support MgO can inhibit the hydrogenation reaction of benzene rings, improve the selectivity of phenol, and at the same time reduce the formation of carbon deposits during the reaction, thus extending the catalyst lifetime. By controlling the synthesis conditions of the catalyst support MgO, the number of basic sites and surface defects on the MgO surface is regulated, thereby affecting the adsorption and desorption behavior of guaiacol and phenol, and thus improving the catalytic performance of guaiacol hydrogenation and deoxygenation. The acidity and basicity of the catalyst surface are further regulated by modifying Pt / MgO with alkali metals, so as to achieve high reaction selectivity and high yield of phenol.

[0034] (2) The hydrogenation and deoxygenation reaction conditions of guaiacol in this invention are relatively mild. The use of a lower hydrogen partial pressure can suppress the hydrogenation reaction of benzene ring, which is conducive to the generation of aromatic compounds such as phenol and improves the selectivity and yield of phenol. Attached Figure Description

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

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

[0037] Unless otherwise specified, all reagents and equipment used in the embodiments are existing technologies.

[0038] Examples 1-4 show how the molar ratio of urea to magnesium during the preparation of the MgO catalyst support was varied to control the number of basic sites and surface defects on the MgO surface. The effects on the catalytic performance of the Pt / MgO catalyst were investigated.

[0039] Example 1

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

[0041] (1) Preparation of MgO support: 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 approximately 5800, available from Maclean's Reagent Company) was added and ultrasonically dispersed evenly. Then, urea was added to make the molar ratio of urea to magnesium nitrate 2:1, and the mixture was thoroughly mixed and dispersed evenly. Subsequently, the mixture was hydrothermally dried in an oven at 120 °C for 24 h, filtered and washed to obtain the precipitate, dried, and then calcined at 500 °C for 4 h in an O2 / Ar (20 / 40 mL / min) atmosphere to obtain the MgO support.

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

[0043] The above-mentioned Pt / MgO catalyst is used in the preparation of phenol in a batch reaction, and the specific steps are as follows:

[0044] (1) Take a mechanically stirred high-pressure reactor, add 440mg of guaiacol, 30ml of n-decane, 220mg of internal standard dodecane (used as an internal reference standard for quantitative analysis), and 150mg of catalyst. Tighten the reactor and check the airtightness of the device. After ensuring that the device is airtight, introduce 0.1MPa H2, stir at 800rpm, and set the temperature to 280℃ for 4h.

[0045] (2) After the reaction is complete, 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 at the start of the reaction - Amount of guaiacol at the end of the reaction) / Amount of guaiacol at the start of the reaction × 100%

[0048] Phenol yield = (Amount of phenol at the end of the reaction / Amount of guaiacol at the beginning of the reaction) × 100%

[0049] Phenol selectivity = Phenol yield / Guaiacol conversion rate × 100%

[0050] Example 2

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

[0052] The application of the above-mentioned Pt / MgO catalyst in the preparation of phenol follows the same method as 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 support prepared in this embodiment is shown below. Figure 1 As shown, its microstructure is granular and flake-like.

[0055] Example 3

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

[0057] The application of the above-mentioned Pt / MgO catalyst in the preparation of phenol follows the same method as 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, as described in Example 1, except that: in step (1) the MgO support preparation method, the molar ratio of urea to magnesium nitrate is 15:1; other steps and conditions are the same as in Example 1.

[0061] The application of the above-mentioned Pt / MgO catalyst in the preparation of phenol follows the same method as 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] Table 1 compares the reaction results of Examples 1-4. It shows that as the molar ratio of urea to magnesium increases during the preparation of the catalyst support MgO, the conversion rate of guaiacol and the yield of phenol both continuously improve. 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. This indicates that the MgO synthesized with a urea to magnesium molar ratio of 10:1 exhibits better catalytic activity with the Pt / MgO catalyst, achieving a guaiacol conversion rate of up to 62.2%. This may be attributed to the greater number of basic sites and surface defects on the surface of the MgO synthesized with a urea to magnesium molar ratio of 10:1. The numerous basic sites on the MgO surface may strongly bind with the hydrogen atoms of the acidic phenolic hydroxyl groups in guaiacol at the metal support interface, which may facilitate the preferential adsorption of guaiacol, thereby indirectly activating C. aryl -OCH3 bonds accelerate the formation of phenol from guaiacol HDO.

[0067] Examples 3 and 5-8 illustrate the catalytic hydrogenation reaction of guaiacol under different reaction pressures.

[0068] Examples 5-8

[0069] A method for preparing a Pt / MgO catalyst is the same as 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 under different reaction pressures

[0073]

[0074] The reaction results from Examples 3 and 5-8 show that a H2 pressure of 0.1 MPa exhibits good catalytic activity, with a phenol selectivity reaching 85.4%. As the H2 pressure increases, the conversion rate of guaiacol decreases, and the yield of phenol declines. Further increasing the pressure will cause phenol to undergo further hydrogenation to cyclohexanol and cyclohexanone. A H2 pressure of 0.1 MPa is favorable for the Pt / MgO catalyst to catalyze the directed conversion of guaiacol to phenol. Therefore, a hydrogen pressure of 0.1 MPa was selected for the reaction.

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

[0076] Examples 9-12

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

[0078] (1) Preparation of MgO support: 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 approximately 5800, available from Maclean's Reagent Company) was added and ultrasonically dispersed evenly. Then, urea was added to make the molar ratio of urea to magnesium nitrate 10:1, and the mixture was thoroughly mixed and dispersed evenly. Subsequently, the mixture was hydrothermally dried in an oven at 120 °C for 24 h, filtered and washed to obtain the precipitate, dried, and then calcined at 500 °C for 4 h in an O2 / Ar (20 / 40 mL / min) atmosphere to obtain the MgO support.

[0079] (2) The modification of the MgO support with different alkali metals (Li, Na, K, Cs) was carried out by the impregnation method. 1 g of MgO support was immersed in 4 mL of alkali metal nitrate aqueous solution with a concentration of 0.572 mol / L for 8 h at room temperature, dried, and calcined at 500 °C for 4 h in O2 / Ar (20 / 40 mL / min) atmosphere to obtain MgO support loaded with alkali metal elements; 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: 0.02 g H2PtCl6·6H2O was dissolved in 70 mL of methanol, and then 1.0 g M / MgO was slowly added to the above metal salt solution. The resulting suspension was stirred at room temperature for 8 h. 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 12 h. Finally, the prepared catalyst was reduced by heating to 400 °C with hydrogen (40 mL / min) at a rate of 10 °C / min for 2 h for later use.

[0081] The above-mentioned catalyst for the catalytic hydrogenation of guaiacol to phenol is used in the preparation of phenol in a batch reaction, and the specific steps are as follows:

[0082] (1) Take a mechanically stirred high-pressure reactor, add 440mg guaiacol, 30ml n-decane, 220mg internal standard dodecane and 150mg catalyst to it, tighten the reactor and check the airtightness of the device. After ensuring that the device does not leak, introduce 0.1MPa H2, stir at 800rpm, and set the temperature to 280℃ for 4h.

[0083] (2) After the reaction is complete, 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 catalysts modified with different alkali metals (Li, Na, K, Cs).

[0086]

[0087] As can be seen from Examples 3 and 9-12, the addition of alkali metal promoters Na and Li improves catalyst activity. In particular, after modification with Na, the conversion rate of guaiacol increases to 87.8%, and the selectivity of phenol reaches 90.7%. This may be because the number and intensity of alkaline sites on the surface of the Pt / MgO catalyst change after modification with alkali metal Na, thus increasing the phenol yield.

[0088] Examples 13-16: Catalysts with different sodium modification amounts used in the hydrodeoxygenation reaction of guaiacol.

[0089] Examples 13-16

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

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

[0092] Step (2) is the same as step (2) in 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) in Example 10. The obtained catalyst 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 application of the catalyst used in the catalytic hydrogenation of guaiacol to prepare phenol is the same as in Example 10.

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

[0096] Table 4. Catalyst reaction results with different sodium modification amounts

[0097]

[0098] As shown in Examples 13-16, modification with alkali metal sodium significantly improved catalytic activity. With increasing sodium modification amount, both the guaiacol conversion and phenol yield showed a trend of first increasing and then decreasing. When the sodium modification amount was 5 wt.%, it exhibited high catalytic activity, with the guaiacol conversion increasing to 87.8% and the phenol selectivity reaching 90.7%. This may be because alkali metal sodium modification increased the basicity of the support, which is conducive to phenol formation.

[0099] Catalytic hydrogenation of guaiacol was carried out at different reaction temperatures in Examples 10 and 17-21.

[0100] Examples 17-21

[0101] A method for preparing a catalyst for the catalytic hydrogenation of guaiacol to phenol is the same as in Example 10.

[0102] The above-mentioned catalyst for the catalytic hydrogenation of guaiacol to prepare phenol is used in the preparation of phenol 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 at different reaction temperatures

[0105]

[0106] Table 6 shows that the reactivity and phenol yield increase with increasing reaction temperature. The results indicate that high temperature promotes the breaking of CO bonds, thereby promoting phenol formation.

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

[0108] Examples 22-24

[0109] A method for preparing a catalyst for the catalytic hydrogenation of guaiacol to phenol is the same as in Example 21.

[0110] The above-mentioned catalyst for the catalytic hydrogenation of guaiacol to prepare phenol is used in the preparation of phenol as described in Example 21, except that the reaction times are 2, 6 and 8 hours respectively.

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

[0112] Table 6 Results for different reaction times

[0113]

[0114] As can be seen from Examples 22-24, under the conditions of 300℃ and 0.1MPa H2, extending the reaction time increases the conversion rate of guaiacol and the yield of phenol. When the reaction time is 6h, the conversion rate of guaiacol can reach 95% and the yield of phenol is 87.2%. However, when the reaction time is extended to 8h, the selectivity of phenol decreases, indicating that as the reaction time is extended, phenol will continue to react and further hydrogenate to generate cyclohexanone and cyclohexanol. Therefore, it is necessary to appropriately control the reaction time to improve the yield of phenol.

[0115] Comparative Examples 1 and 2: The types of magnesium salts added during the hydrothermal synthesis of magnesium oxide were changed, and the platinum-catalyzed hydrodeoxygenation reaction of guaiacol was carried out.

[0116] Comparative Examples 1-2

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

[0118] The application of the catalyst used in the catalytic hydrogenation of guaiacol to prepare 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 conversion rate of guaiacol was 76.4% and the selectivity of phenol was 81.8%.

[0121] Comparing Example 23 with Comparative Examples 1 and 2, it can be seen that when magnesium salt is added during the hydrothermal synthesis of magnesium oxide, the catalyst exhibits higher catalytic activity. This may be because the use of magnesium nitrate helps to form uniformly distributed crystals, avoiding agglomeration, thus obtaining a well-dispersed magnesium oxide support with a high specific surface area, providing more active sites, which is beneficial for adsorption and catalytic reactions.

[0122] Comparative Example 3: Magnesium oxide support synthesized by chemical precipitation method, supported by platinum-catalyzed hydrodeoxygenation reaction of guaiacol.

[0123] Comparative Example 3

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

[0125] The application of the catalyst used in the catalytic hydrogenation of guaiacol to prepare 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] Comparing Example 23 and Comparative Example 3, it can be seen that the magnesium oxide Pt-5Na / MgO catalyst synthesized by the hydrothermal method exhibits high catalytic activity. This may be attributed to the regular morphology and large specific surface area of ​​the magnesium oxide particles prepared by the hydrothermal method, which can provide more active sites, making it easier for reactant molecules to adsorb onto the catalyst surface, thereby increasing the contact area between the reactants and the catalyst, improving the rate of the catalytic reaction, and accelerating the catalytic hydrogenation of guaiacol to phenol.

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

[0129] Comparative Example 4

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

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

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

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

[0134] The application of the catalyst used in the catalytic hydrogenation of guaiacol to prepare 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] As seen in Example 23 and Comparative Example 4, different metal impregnation orders affect catalytic performance during catalyst preparation. The catalyst obtained by first modifying the magnesium oxide support with alkali metal sodium and then impregnating it with platinum exhibits better catalytic performance than the catalyst impregnated with platinum first and then with alkali metal sodium. This may be because impregnating with alkali metal sodium first alters the acidity / basicity of the catalyst surface, changing the electronic structure of platinum and thus affecting the catalyst's catalytic performance. The impregnation order may also affect the metal dispersion on the support; uniformly dispersed metal particles generally exhibit higher catalytic activity. Impregnating with alkali metal sodium first regulates the platinum dispersion, promoting uniform distribution of platinum on the support, thus resulting in higher catalytic activity.

[0137] Comparative Example 5: Magnesium oxide-supported alkali metal sodium-catalyzed hydrodeoxygenation reaction of guaiacol

[0138] Comparative Example 5

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

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

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

[0142] The application of the catalyst used in the catalytic hydrogenation of guaiacol to prepare 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 shown in Comparative Example 5, MgO supported only with alkali metal sodium exhibits very low catalytic activity for the hydrogenation of guaiacol, with guaiacol essentially not being converted. The phenol selectivity is only 17.2%, therefore, it is difficult to achieve high phenol yields by supporting only alkali metal sodium.

[0145] The above embodiments are implementation methods adopted by the present invention, but the implementation methods of the present invention are not limited to the above embodiments. Any equivalent substitutions or changes made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solutions and inventive concepts of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A catalyst for the catalytic hydrogenation of guaiacol to phenol, characterized in that, The catalyst is a MgO support loaded with Pt and an alkali metal element, wherein the alkali metal is selected from Li, Na, K or Cs. The method for preparing the catalyst for the catalytic hydrogenation of guaiacol to phenol includes the following steps: (1) Magnesium nitrate, P123 and urea are fully dissolved in deionized water, and after hydrothermal reaction, the MgO carrier is obtained by filtration, washing, drying and calcination. (2) The MgO support is immersed in an aqueous solution of alkali metal nitrate, and then dried and calcined to obtain the MgO support loaded with alkali metal elements; the alkali metal is selected from Li, Na, K or Cs. (3) The MgO support loaded with alkali metal elements was immersed in a methanol solution of chloroplatinic acid, the methanol was removed, the mixture was dried, and then reduced to obtain a catalyst for the catalytic hydrogenation of guaiacol to prepare phenol.

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

1.

3. The catalyst for the catalytic hydrogenation of guaiacol to phenol according to claim 2, characterized in that, The molar ratio of urea to magnesium nitrate is 5-10:

1.

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

5. The catalyst for the catalytic hydrogenation of guaiacol to phenol according to claim 1, characterized in that, In step (2), the alkali metal is Li or Na.

6. The catalyst for the catalytic hydrogenation of guaiacol to phenol according to claim 1, characterized in that, In step (2), the concentration of the alkali metal nitrate aqueous solution is 0.1-1.2 mol / L.

7. The catalyst for the catalytic hydrogenation of guaiacol to phenol according to claim 6, characterized in that, The concentration of aqueous solution of alkali metal nitrates is 0.3-0.6 mol / L.

8. The catalyst for the catalytic hydrogenation of guaiacol to phenol according to claim 1, characterized in that, In step (2), the mass ratio of the MgO support to the volume ratio of the alkali metal nitrate aqueous solution is 0.125-0.25 g / mL.

9. The catalyst for the catalytic hydrogenation of guaiacol to phenol according to claim 1, characterized in that, Step (2) includes one or more of the following conditions: i. Immersion temperature is room temperature, immersion time is 6-10 hours; ii. The calcination temperature is 400-600℃, the calcination time is 2-4 h, and the calcination atmosphere is a mixture of O2 and Ar, wherein the volume ratio of O2 to Ar is 1:1-3.

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

11. The application of the catalyst for the catalytic hydrogenation of guaiacol to phenol as described in claim 1 in the preparation of phenol; the application method is as follows: in n-decane solvent, under the action of the above catalyst, guaiacol reacts with H2 to obtain phenol.

12. The application according to claim 11, characterized in that, 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℃, the hydrogen pressure is 0.1-1 MPa, the reaction time is 2-8 h, and the reaction is carried out under stirring conditions.

13. The application according to claim 12, characterized in that, The reaction temperature is 280-300℃, and the reaction time is 4-8h.

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