Method for preparing 2-methallyl alcohol from methylacrolein

Abstract

The invention discloses a method for preparing 2-methallyl alcohol from methylacrolein, which comprises the following steps: in a hydrogen atmosphere, pre-reducing a catalyst, and then contacting with methylacrolein to react I to generate 2-methallyl alcohol, the catalyst is an oxygen vacancy-rich metal silver catalyst; in the oxygen vacancy-enriched metallic silver catalyst, the loading capacity of metallic silver is 2-20wt.%, and the loading capacity of the metallic silver is metered by the mass of the silver element. By matching with a continuous reactor-fixed bed, the production efficiency of the 2-methallyl alcohol is greatly improved. Under the conditions that hydrogen is used as a reducing agent and no solvent exists, the silver metal catalyst shows extremely high methylacrolein conversion rate and 2-methylallyl alcohol selectivity, and meanwhile, the catalyst can stably operate for a long time.

Description

Technical Field

[0001] The present application relates to a method for preparing 2-methylpropenol from methacrolein, belonging to the field of chemical engineering technology. Background Art

[0002] Unsaturated alcohols are widely used in the production processes of fields such as pesticides, daily chemicals, and food flavoring agents, and are a very important class of chemical intermediates. However, the complex preparation process and harsh production environment limit their yield, and at the same time, it will also lead to a relatively high production price. Taking 2-methylpropenol as an example, 2-methylpropenol is an important intermediate for preparing polymer monomers, surfactants, synthetic resin additives, and polycarboxylic acid superplasticizers. Currently, the methods for preparing 2-methylpropenol industrially can be classified into the chlor-alkali method, hydrogen transfer method, dehydration method, and selective hydrogenation method according to the reaction mechanism. Among them, the chlor-alkali method is the most main method for industrially producing 2-methylpropenol. This method uses isobutene and chlorine as reactants, first generates isobutene chloride, and then undergoes a hydroxyl substitution reaction under alkaline conditions to generate 2-methylpropenol. The biggest drawback of this process is that the reaction conditions are relatively harsh, and the separation of products and the recovery of solvents are relatively difficult. At the same time, a large amount of by-product ethers will be generated during the reaction process, which will further increase the difficulty of separation. More notably, the use of chlorine not only poses higher requirements for the safety of the process, but also increases the investment in equipment. In comparison, selective hydrogenation is a more environmentally friendly process. However, this process is extremely dependent on catalysts. Therefore, developing a catalyst with high activity and high selectivity has become the top priority for improving the production efficiency of this process. For this reason, we have constructed a metal catalyst with surface oxygen defects for the continuous production of 2-methylpropenol under gas-phase conditions. Summary of the Invention

[0003] The present invention innovatively improves some deficiencies in the prior art by designing a good catalyst preparation method and reasonably designing and optimizing the reaction process. Characteristically, a series of supported catalysts with defect sites on the surface are prepared to selectively adsorb and activate carbonyl sites.

[0004] According to one aspect of the present application, there is provided a method for preparing 2-methylpropenol from methacrolein, the method comprising:

[0005] Pre-reducing the catalyst in a hydrogen atmosphere, and then contacting it with methacrolein to carry out Reaction I to generate 2-methylpropenol;

[0006] The catalyst is a metal silver catalyst rich in oxygen vacancies;

[0007] The metal silver catalyst rich in oxygen vacancies comprises active component I and active component II;

[0008] The active component I is silver;

[0009] The active component II is selected from at least one of titanium, cerium, and zirconium.

[0010] Optionally, in the oxygen-rich vacancy silver-based catalyst, the loading amount of silver metal is 2-20 wt.%, and the loading amount of silver metal is calculated based on the mass of silver element.

[0011] Optionally, in the oxygen-rich vacancy silver-based catalyst, the loading amount of silver metal is independently selected from any value among 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.%, 10 wt.%, 12 wt.%, 14 wt.%, 16 wt.%, 18 wt.%, 20 wt.% or the range value between any two of the above.

[0012] Optionally, the preparation method of the oxygen-rich vacancy silver-based catalyst includes:

[0013] In a closed reactor, a mixture containing a silver source, other metal sources, and a surfactant is reacted, dried, and calcined to obtain the oxygen-rich vacancy silver-based catalyst;

[0014] The other metal source is selected from at least one of a titanium source, a cerium source, and a zirconium source.

[0015] Optionally, the silver source is selected from at least one of silver nitrate, silver sol, and triphenyl silver.

[0016] Optionally, the titanium source is selected from at least one of tetrabutyl titanate, titanium tert-butoxide, and metatitanic acid.

[0017] Optionally, the cerium source is selected from cerium nitrate and / or cerium acetate.

[0018] Optionally, the zirconium source is selected from at least one of zirconyl nitrate, zirconium nitrate, and zirconyl chloride.

[0019] Optionally, the surfactant is selected from at least one of CTAB, F127, P123, and PVP.

[0020] Optionally, the molar ratio of the silver source to the other metal source is 1000-0.01.

[0021] Optionally, the mass ratio of the silver source to the surfactant is 1000:1-0.01.

[0022] Optionally, the mixture further includes an emulsion-forming aid, a metal ion chelating agent, and a solvent.

[0023] Optionally, the emulsion-forming aid is selected from at least one of C6-C16 alkanes.

[0024] Optionally, the metal ion chelating agent is selected from at least one of diethylenetriamine, aniline, and citric acid.

[0025] Optionally, the solvent is selected from at least one of ethanol, ethylene glycol, and water.

[0026] Optionally, the mass-volume ratio of the silver source to the co-emulsifier is 1:100 to 1.

[0027] Optionally, the mass ratio of the silver source to the metal ion chelating agent is 1:1000 to 1.

[0028] Optionally, the volume ratio of the co-emulsifier to the solvent is 1:100 to 1:1.

[0029] Optionally, the volume ratio of the co-emulsifier to the solvent is independently selected from any value of 1:100, 1:80, 1:60, 1:40, 1:20, 1:10, 1:5, 1:1 or the range value between any two of the above.

[0030] Optionally, the temperature of Reaction II is 50 to 200 °C, and the time of Reaction II is 2 to 24 h.

[0031] Optionally, the temperature of Reaction II is independently selected from any value of 50 °C, 80 °C, 100 °C, 150 °C, 180 °C, 200 °C or the range value between any two of the above.

[0032] Optionally, the time of Reaction II is independently selected from any value of 2 h, 4 h, 8 h, 10 h, 12 h, 16 h, 18 h, 24 h or the range value between any two of the above.

[0033] Optionally, the temperature of drying is 30 to 150 °C, and the time of drying is 2 to 24 h.

[0034] Optionally, the temperature of calcination is 200 to 800 °C, and the time of calcination is 1 to 2 h.

[0035] Optionally, the atmosphere of calcination is selected from at least one of nitrogen atmosphere, air atmosphere, and carbon dioxide atmosphere.

[0036] Optionally, before the reaction, the pH of the mixture needs to be adjusted.

[0037] Optionally, when adjusting the pH, the pH adjusting agent is selected from at least one of ammonia water, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

[0038] Optionally, when adjusting the pH, the pH adjusting temperature is 20 to 100 °C.

[0039] Optionally, when adjusting the pH, the pH adjustment temperature is independently selected from any value of 20°C, 40°C, 50°C, 70°C, 80°C, 100°C or the range value between any two of the above.

[0040] Optionally, the temperature of the pre-reduction is 200 - 800°C, and the time of the pre-reduction is 1 - 3 h.

[0041] Optionally, the mass hourly space velocity of methacrolein is 0.5 - 5 h -1 。

[0042] Optionally, the mass hourly space velocity of methacrolein is independently 0.5 h -1 、1 h -1 、1.5 h -1 、2 h -1 、2.5 h -1 、3 h -1 、3.5 h -1 、4 h -1 、5 h -1 or the range value between any two of the above.

[0043] Optionally, the temperature of Reaction I is 50 - 250°C.

[0044] Optionally, the temperature of Reaction I is independently any value of 50°C, 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, 250°C or the range value between any two of the above.

[0045] Optionally, the molar ratio of hydrogen to methacrolein is 1 - 20:1.

[0046] Optionally, the molar ratio of hydrogen to methacrolein is independently selected from any value of 1:1, 2:1, 5:1, 10:1, 15:1, 20:1 or the range value between any two of the above.

[0047] As an optional technical implementation manner, the present application is realized through the following technical solutions:

[0048] Solution 1 adopted in the present invention:

[0049] (1) Dissolve a certain mass of silver nitrate, cerium nitrate or cerium acetate and non-ionic surfactant F127 in a certain amount of deionized water. The loading amount of metallic silver is calculated based on silver metal, and the loading amount is between 1 - 20%.

[0050] (2) Add the above metal salt solution to a certain amount of ethylene glycol and heptane, and stir vigorously, where the volume ratio of ethylene glycol to heptane is between 100 - 1.

[0051] (3) Hydrothermally treat the above mixture, transfer it to a hydrothermal reactor and maintain it at a certain temperature between 50 and 200 °C for 2 to 24 h.

[0052] (4) Clean with one or several of anhydrous ethanol, deionized water or dilute hydrochloric acid, and the cleaning temperature is between 25 and 80 °C.

[0053] (5) Dry the obtained sample at 120 °C for 24 h, and then calcine the sample at 300 to 500 °C for 2 h.

[0054] (6) Reduce the calcined catalyst with hydrogen at 200 to 500 °C for 2 h, and then passivate the reduced sample with carbon dioxide at 20 to 200 °C.

[0055] (7) Shape the treated catalyst and then use it for the production of unsaturated alcohols. The reaction temperature is between 50 and 250 °C, the space velocity is between 0.5 and 5 h -1 and the ratio of hydrogen to methacrolein is between 1 and 20.

[0056] Scheme 2 adopted in the present invention:

[0057] (1) Dissolve a certain mass of zirconyl nitrate, zirconium nitrate or zirconyl chloride in a certain amount of anhydrous ethanol or deionized water.

[0058] (2) Add a certain amount of silver nitrate and diethylenetriamine to the above solution, and vigorously stir the solution at 20 to 80 °C for 20 h. The silver loading is calculated based on silver metal, and the loading is between 1 and 20%, and the molar ratio of diethylenetriamine to silver metal ions is between 10 and 1.

[0059] (3) Dissolve one or two of a certain mass of cationic surfactant CTAB and non-ionic surfactant F127 in ammonia water with a concentration of 1 mol / L, and slowly drip the solution into the metal salt solution.

[0060] (4) Let it stand for a while. When the pH value of the mixture is at a certain value between 7 and 9, transfer the mixture to a hydrothermal reactor and maintain it at 60 to 180 °C for 8 to 24 h.

[0061] (5) After the hydrothermal reactor cools to room temperature, filter out the precipitate and wash it three times with one or several of deionized water, anhydrous ethanol or dilute hydrochloric acid solution.

[0062] (6) Dry the obtained sample at 120 °C for 24 h, and then calcine the sample at 300 to 500 °C for 2 h.

[0063] (7) The calcined catalyst is reduced with hydrogen at 200 - 500 °C for 2 h, and then the reduced sample is passivated with carbon dioxide at 20 - 200 °C.

[0064] (8) The treated catalyst is formed and then used for the production of unsaturated alcohols. The reaction temperature is between 50 - 250 °C, the space velocity is between 0.5 - 5 h -1 -1, and the ratio of hydrogen to methacrolein is between 1 - 20.

[0065] Scheme three adopted in the present invention:

[0066] (1) A certain amount of cationic surfactant CTAB is dissolved in deionized water, and then 10 ml of hexadecane and 200 ml of ethanol are added thereto.

[0067] (2) 35 wt% ammonia water is added to the above solution to adjust the pH value of the solution to about 11, and it is vigorously stirred for 20 min.

[0068] (3) A certain amount of tetraethyl orthosilicate / ethanol mixed solution is slowly added to the above solution, and then it is stirred at 20 - 80 °C for 20 h.

[0069] (4) The mixture is centrifuged and dried at 60 °C for 24 h.

[0070] (5) A certain amount of silver nitrate is dissolved in deionized water, and then it is impregnated into the silica microspheres. After the impregnated sample is left standing for 24 h, it is dried at 120 °C for 24 h, and then calcined at 350 °C for 2 h.

[0071] (6) The calcined sample is added to anhydrous ethanol, and it is vigorously stirred. Then a certain amount of tetrabutyl titanate is added, and it is vigorously stirred at 20 - 100 °C for 10 min.

[0072] (7) Ammonia water of 1 mol / L is introduced at a rate of 1 ml / min. When the pH reaches 7, the above mixture is filtered.

[0073] (8) Subsequently, the precipitate is added to 1 mol / L NaOH solution and stirred at 30 °C for 24 h, and then filtered again. It is washed 3 times with deionized water at 25 °C, and then dried at 120 °C for 24 h. The dried sample is calcined at 500 °C for 2 h.

[0074] (9) The calcined catalyst is reduced with hydrogen at 200 - 500 °C for 2 h, and then the reduced sample is passivated with carbon dioxide at 20 - 200 °C.

[0075] (10) The processed catalyst is formed and then used for the production of unsaturated alcohols. The reaction temperature is between 50 and 250 °C, and the space velocity is between 0.5 and 5 h -1 -1, and the ratio of hydrogen to methacrolein is between 1 and 20.

[0076] This application discloses a preparation method and application of a silver catalyst supported on an oxygen-rich vacancy carrier. The preparation process includes a series of processes such as crystallization, self-assembly, and nano-encapsulation. This application greatly improves the production efficiency of 2-methylallyl alcohol by adapting to a continuous reactor-fixed bed. Under the conditions of using hydrogen as a reducing agent and no solvent, the silver metal catalyst shows extremely high conversion of methacrolein and selectivity of 2-methylallyl alcohol, and at the same time, the catalyst can operate stably for a long time.

[0077] The beneficial effects that this application can produce include:

[0078] The Ag catalyst provided by this application is a relatively inexpensive catalyst compared to noble metal catalysts such as Pt, Pd, Ru, Rh, and Ir. The unique valence electron structure of metallic Ag makes it have a special carbonyl adsorption configuration, and the fully electron-loaded d orbital reduces the adsorption ability for the C═C bond; by interacting metal nanoparticles with a specially constructed catalyst carrier, the synergistic effect between the active site and the carrier functional site can be constructed, effectively improving the selectivity of unsaturated alcohols; this method improves the currently highly developed liquid-phase hydrogenation method. Through the optimization of the reaction process, gas-phase hydrogenation under solvent-free conditions is realized, which can effectively improve the production efficiency, and at the same time eliminate the industrial pollution and energy consumption generated in the separation process of the solvent and the product, which not only better meets the requirements of environmental protection but also reduces the production cost. Description of the Drawings

[0079] Figure 1 It is the infrared adsorption spectrum of methacrolein of the catalysts in Examples 1 to 3 of this application. Detailed Embodiments

[0080] The following details this application with reference to the embodiments, but this application is not limited to these embodiments.

[0081] Unless otherwise specified, the raw materials in the embodiments of this application are all purchased through commercial channels.

[0082] In the embodiments of this application, a PE company infrared spectrometer is used for adsorption state characterization.

[0083] Conversion rate = 1 - amount of unreacted reactant substance / total amount of reactant substance.

[0084] Selectivity = amount of product formed / amount of reactant converted.

[0085] Example 1

[0086] Dissolve 0.3 g of silver nitrate, 0.8 g of cerium nitrate and 0.15 g of F127 in 10 ml of deionized water, and stir vigorously for 30 min until foam appears to form Solvent A; dissolve 0.5 g of CTAB in 10 ml of deionized water, and add 200 ml of ethylene glycol and 10 ml of heptane thereto and stir vigorously until a microemulsion is formed, which is Solvent B. Slowly add Solvent A to Solvent B and stir vigorously. Transfer the above mixed liquid into a hydrothermal reactor and maintain it at 180 °C for 24 h. After the hydrothermal reactor is cooled to room temperature, wash it 3 times with 2 vol% HCl at 50 °C, then wash it 3 times with deionized water at 25 °C, then dry it at 120 °C for 24 h, and calcine the dried sample at 500 °C for 2 h. The calcined sample is reduced in a hydrogen atmosphere at 400 °C for 2 h, and after the sample is cooled to room temperature, carbon dioxide is introduced to passivate the catalyst. Press and crush the reduced catalyst into 20 - 40 mesh, load it into a fixed-bed reactor and pre-reduce it with hydrogen at 300 °C for 2 h. Wait for the fixed-bed reactor to cool to 180 °C, and introduce methacrolein with a space velocity of 2 h -1 , where the ratio of hydrogen to methacrolein is 10:1, and the specific experimental results are shown in Table 1.

[0087] Example 2

[0088] Dissolve 9.38 g of zirconyl nitrate in 300 ml of absolute ethanol, and add 0.414 g of silver nitrate and 0.75 g of diethylenetriamine to this solution, and stir the solution vigorously at 60 °C for 20 h. Dissolve 3 g of CTAB and 1 g of F127 in 100 ml of ammonia water (1 mol / L), and slowly introduce this solution into the ethanol solvent dissolved with metal salts at a rate of 1 ml / min. When the pH value drops to about 9, transfer the above mixture into a hydrothermal reactor and maintain it at 90 °C for 24 h. After the hydrothermal reactor is cooled to room temperature, wash it 3 times with 2 vol% HCl at 50 °C, then wash it 3 times with deionized water at 25 °C, then dry it at 120 °C for 24 h, and calcine the dried sample at 500 °C for 2 h. The calcined sample is reduced in a hydrogen atmosphere at 400 °C for 2 h, and after the sample is cooled to room temperature, carbon dioxide is introduced to passivate the catalyst. Press and crush the reduced catalyst into 20 - 40 mesh, load it into a fixed-bed reactor and pre-reduce it with hydrogen at 300 °C for 2 h. Wait for the fixed-bed reactor to cool to 180 °C, and introduce methacrolein with a space velocity of 2 h -1 , where the ratio of hydrogen to methacrolein is 10:1, and the specific experimental results are shown in Table 1.

[0089] Example 3

[0090] Dissolve 0.193 g of CTAB in 98 ml of deionized water, and then slowly add a mixed solution of 10 g of hexadecane / 200 ml of ethanol at 50 °C. Add 0.8 g of 35 wt% ammonia water to the above solution to adjust the pH value to 11. After vigorously stirring for 20 min, add 10 g of 20 wt% tetraethyl orthosilicate / ethanol solution to the above mixture, and continue stirring at 50 °C for 20 hours. Then, centrifuge the obtained mixture and dry it at 60 °C for 24 h. Dissolve 0.414 g of silver nitrate in 6 ml of deionized water, and then impregnate it into the prepared silica microspheres, dry it at 120 °C for 24 h, and then calcine it at 350 °C for 2 h. Add 300 ml of absolute ethanol and 18 g of tetrabutyl titanate to the above calcined sample, vigorously stir at 50 °C for 10 min, and then introduce 1 mol / L ammonia water at a rate of 1 ml / min. When the pH reaches 7, filter the above mixture. Then add the precipitate to 1 mol / L NaOH solution, stir at 30 °C for 24 h, and then filter again. Wash it 3 times with deionized water at 25 °C, and then dry it at 120 °C for 24 h. Calcinate the dried sample at 500 °C for 2 h. The calcined sample is reduced in a hydrogen atmosphere at 400 °C for 2 h. After the sample is cooled to room temperature, introduce carbon dioxide to passivate the catalyst. Press the reduced catalyst into tablets, crush it into 20 - 40 mesh, and load it into a fixed-bed reactor and pre-reduce it with hydrogen at 300 °C for 2 h. Wait for the fixed-bed reactor to cool to 180 °C, and introduce methacrolein with a space velocity of 2 h -1 , where the ratio of hydrogen to methacrolein is 10:1. The specific experimental results are shown in Table 1.

[0091] Table 1 Activity evaluation results in Examples 1 - 3

[0092]

[0093] It can be seen from Table 1 that the catalysts prepared by the described specific preparation method all exhibit good activity and selectivity for the target product.

[0094] From Figure 1 it can be seen that ( Figure 1 Example 1 in

[0095] Corresponds to Example 1, Example 2 corresponds to Example 2, and Example 3 corresponds to Example 3) the existence of oxygen vacancies affects the adsorption configuration of the carbon-based group and promotes the activation of the C=O bond.

[0096] Dissolve 0.3 g of silver nitrate and 17 g of tetraethyl orthosilicate in 300 ml of ethanol. Slowly add 100 ml of 5% ammonia water to the above solution, filter and wash it three times. Place the filter cake in an oven at 120 °C and dry it for 24 h. Calcinate the dried sample at 500 °C for 2 h. Reduce the calcined sample at 400 °C in a hydrogen atmosphere for 2 h. After the sample cools to room temperature, pass carbon dioxide to passivate the catalyst. Press and crush the reduced catalyst into 20-40 mesh, and load it into a fixed-bed reactor. Pre-reduce it with hydrogen at 300 °C for 2 h. Wait for the fixed-bed reactor to cool to 180 °C, and pass methacrolein with a space velocity of 2 h -1 , where the ratio of hydrogen to methacrolein is 10:1. The specific experimental results are shown in Table 1.

[0097] As described above, only several embodiments of the present application are given, and the present application is not limited in any form. Although the present application is disclosed by preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing 2-methylpropenol from methacrolein, characterized in that, the method comprises: in a hydrogen atmosphere, pre-reducing the catalyst, then contacting it with methacrolein, and reacting I to produce 2-methylpropenol; the catalyst is an oxygen-rich vacancy silver metal catalyst; the oxygen-rich vacancy silver metal catalyst comprises active component I and active component II; the active component I is silver; the active component II is selected from at least one of titanium, cerium, and zirconium.

2. The method according to claim 1, characterized in that, in the oxygen-rich vacancy silver metal catalyst, the loading amount of silver metal is 2-20 wt.%, and the loading amount of silver metal is calculated based on the mass of silver element.

3. The method according to claim 1, characterized in that, the preparation method of the oxygen-rich vacancy silver metal catalyst comprises: in a closed reactor, reacting a mixture containing a silver source, a metal source of active component II, and a surfactant, drying, and calcining to obtain the oxygen-rich vacancy silver metal catalyst; the metal source of active component II is selected from at least one of a titanium source, a cerium source, and a zirconium source.

4. The method according to claim 3, characterized in that, the silver source is selected from at least one of silver nitrate, silver sol, and triphenylsilver; preferably, the titanium source is selected from at least one of tetrabutyl titanate, titanium tert-butoxide, and metatitanic acid; preferably, the cerium source is selected from cerium nitrate and / or cerium acetate; preferably, the zirconium source is selected from at least one of zirconyl nitrate, zirconium nitrate, and zirconyl chloride.

5. The method according to claim 3, characterized in that, the surfactant is selected from at least one of CTAB, F127, P123, and PVP; preferably, the molar ratio of the silver source to the other metal source is 1000-0.01; preferably, the mass ratio of the silver source to the surfactant is 1000:1-0.

01.

6. The method according to claim 3, characterized in that, the mixture further comprises an emulsion-forming aid, a metal ion chelating agent, and a solvent; preferably, the emulsion-forming aid is selected from at least one of C6-C16 alkanes; preferably, the metal ion chelating agent is selected from at least one of diethylenetriamine, aniline, and citric acid; preferably, the solvent is selected from at least one of ethanol, ethylene glycol, and water.

7. The method according to claim 6, characterized in that, the mass-volume ratio of the silver source to the emulsion-forming aid is 1:100-1; preferably, the mass ratio of the silver source to the metal ion chelating agent is 1:1000-1; preferably, the volume ratio of the emulsion-forming aid to the solvent is 1:100-1:

1.

8. The method according to claim 3, characterized in that, the temperature of reaction II is 50-200 °C, and the time of reaction II is 2-24 h; preferably, the temperature of drying is 30-150 °C, and the time of drying is 2-24 h; preferably, the temperature of calcining is 200-800 °C, and the time of calcining is 2-24 h; preferably, the non-active atmosphere for calcining is selected from at least one of a nitrogen atmosphere, an air atmosphere, and a carbon dioxide atmosphere.

9. The method according to claim 3, wherein, before the reaction, the mixture needs to be pH-adjusted; preferably, when performing the pH adjustment, the pH adjuster used is selected from at least one of ammonia water, sodium hydroxide, sodium carbonate, and sodium bicarbonate; preferably, when performing the pH adjustment, the pH adjustment temperature is 20-100 °C.

10. The method according to claim 1, wherein, the temperature of the pre-reduction is 200-800 °C, and the time of the pre-reduction is 1-3 h; Preferably, the mass hourly space velocity of the methacrolein is 0.5 to 5 h -1 ; preferably, the temperature of the reaction I is 50-250 °C; preferably, the molar ratio of hydrogen to methacrolein is 1-20:1.

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