Preparation method of magnesium-aluminum composite oxide-based catalyst and application of magnesium-aluminum composite oxide-based catalyst in preparation of anisole
By employing anionic and cation-hydrolysis and porous oxide coating technology, the problems of uniformity and particle morphology in the preparation process of magnesium-aluminum composite oxide catalysts were solved, thereby improving the catalyst activity and the efficiency of phenol methylation reaction, and realizing the production of anisole at low cost and high yield.
Patent Information
- Application Number
- CN202512006587.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-03-17
Smart Images
Figure CN121669210A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the field of new preparation methods of magnesium-aluminum hydrotalcite, and particularly relates to a preparation method of a magnesium-aluminum composite oxide-based catalyst and application of the catalyst in preparation of anisole. BACKGROUND
[0002] Under the background of accelerating global carbon neutralization, the green transformation of the anisole industry has become an inevitable trend. Compared with the traditional dimethyl sulfate process, the DMC method has become a benchmark technology for low-carbon production due to its high atom economy and only methanol and CO2 as byproducts. As the largest producer in the world, China can reduce carbon emissions by 40% per ton of product by promoting the DMC process, while reducing the pressure of toxic waste disposal. In the future, with the breakthrough of bio-based raw materials (such as lignin-derived phenol) and renewable energy-driven synthesis processes, the anisole industry is expected to achieve a leap from "low pollution" to "zero carbon emission". This transformation not only responds to global climate action, but also provides a "economic-environmental" win-win sustainable development paradigm for the fine chemical industry.
[0003] The traditional synthesis process still limits the sustainable development of the industry in terms of safety production, environmental protection and reaction efficiency. The problem lies in that when the methylation of phenol is good, the reagent usually contains halogen or sulfur, which pollutes the environment, and when the green methylation reagent methanol is used, the selectivity of phenol is low. After improvement, dimethyl carbonate as a methylation reagent meets the requirements of green chemistry.
[0004] In terms of catalyst, the existing mainstream catalyst is prepared by a co-precipitation method to prepare a catalyst precursor magnesium-aluminum hydrotalcite, and then calcined to form a magnesium-aluminum composite oxide. The mixed salt solution of Mg(NO3)2•6H2O and Al(NO3)3•9H2O is needed in the preparation, and the precipitating agent is a mixed aqueous solution of NaOH and Na2CO3. The mixed salt solution and a certain amount of precipitating agent are simultaneously added to a beaker containing deionized water, the dropping speed of the precipitating agent and the salt solution is controlled, and the pH and temperature are maintained. After precipitation, the temperature is raised to 90 ℃ for 4 h, then filtered and washed with deionized water until neutral, dried at 100 ℃ for 12 h, and ground to obtain magnesium-aluminum hydrotalcite, which is calcined at 650 ℃ for 6 h to obtain a magnesium-aluminum composite oxide.
[0005] The main drawback of the above preparation method is the difficulty in precisely controlling the uniformity and particle morphology of the product. Due to the different precipitation rates of different metal ions, uneven product composition is easily caused. Furthermore, during precipitation and drying, nanoparticles are prone to severe agglomeration, resulting in a wide particle size distribution. In addition, this method is highly sensitive to reaction conditions (such as pH and temperature), leading to poor batch-to-batch reproducibility, and subsequent washing and calcination steps can easily introduce impurities or alter the product structure. Summary of the Invention
[0006] To address the challenge of precisely controlling the uniformity and particle morphology of products from existing magnesium-aluminum composite oxides, this invention provides a method for preparing a magnesium-aluminum composite oxide-based catalyst and its application in the preparation of anisole. The catalyst precursor, magnesium-aluminum hydrotalcite, is synthesized using a cation-anion dual hydrolysis method. The catalyst is supported on a magnesium-aluminum composite oxide, with a porous, more basic oxide coated onto the support. The active components include four metals: La, Ba, Mn, and Zr. The resulting catalyst is then evaluated for activity.
[0007] This invention is achieved through the following technical solution: a method for preparing a magnesium-aluminum composite oxide-based catalyst, comprising the following steps: (1) Dissolve magnesium nitrate hexahydrate and sodium aluminate separately in deionized water and stir until dissolved. Keep the sodium aluminate aqueous solution at a certain temperature while stirring, and add magnesium nitrate hexahydrate solution dropwise. After completion, keep the solution at a certain temperature for aging, and then filter, dry and grind to obtain the catalyst precursor magnesium aluminum hydrotalcite. (2) Prepare a metal salt solution with a certain molar concentration, immerse magnesium aluminum hydrotalcite in the solution, heat and stir in a water bath, and repeat the immersion, drying and calcination cycles several times to obtain a magnesium aluminum composite oxide-based catalyst; the metal salt contains at least one of lanthanum, barium, manganese and zirconium metal salts.
[0008] As a further improvement to the preparation method of this invention, the sodium aluminate aqueous solution is kept at a temperature of 40 °C.
[0009] As a further improvement to the preparation method of the present invention, the aging temperature is 90 ℃ and the aging time is 6 h.
[0010] As a further improvement to the preparation method of the present invention, the water bath heating temperature is 90 ℃ and the water bath heating time is 6 h.
[0011] As a further improvement to the preparation method of the present invention, the calcination is carried out under nitrogen atmosphere, the calcination temperature is 600 °C, and the calcination time is 2 h.
[0012] As a further improvement to the preparation method of the present invention, the lanthanum, barium, manganese and zirconium metal salts are all nitrates.
[0013] As a further improvement to the preparation method of the present invention, the molar ratio of metal ions to magnesium and aluminum in the metal salt is 1:1-9:5-18.
[0014] Furthermore, the magnesium-aluminum composite oxide-based catalyst prepared by the aforementioned method is applied in the catalytic methylation reaction of phenol hydroxyl oxygen to generate anisole.
[0015] The anisole synthesis process used in this invention is as follows: Phenol and dimethyl carbonate undergo a methylation reaction on a magnesium-aluminum composite oxide supported by lanthanum, barium, manganese, and zirconium metal oxides, catalyzing the formation of anisole through the methylation of the phenol hydroxyl oxygen. The specific reaction is as follows: Main reaction: C6H6O + (CH3)2CO3 → C7H8O + CH3OH + CO2 Side reaction: C6H6O + 2(CH3)2CO3 → o-CH3C6H4OCH3 + 2CH3OH + 2CO2 C6H6O+2(CH3)2CO3→p-CH3C6H4OCH3+2CH3OH+2CO2 C6H6O+(CH3)2CO3→o-CH3C6H4OH+CO2+CH3OH C6H6O+(CH3)2CO3→C8H8O3+CH3OH By adjusting the reaction process conditions—the temperature of the methylation reaction to generate anisole is 180~200 ℃, and the reaction pressure is atmospheric pressure—the yield of the target product anisole can reach a maximum of about 98.1%.
[0016] The technical solution provided by this invention has the following advantages compared with the prior art: (1) The active components are all transition metals, alkaline earth metals, and rare earth metal oxides, and do not contain precious metals, so the production cost is low. (2) The active components are loaded onto the surface of the magnesium-aluminum composite oxide carrier in a one-step manner, which is simple in process; (3) The active components and the carrier can be burned at 600 °C to form a highly dispersed and highly active composite oxide active layer. Attached Figure Description
[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.
[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a scanning electron microscope image of Example 3.
[0020] Figure 2 This is a transmission electron microscope image of Example 3. Detailed Implementation
[0021] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.
[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.
[0023] The specific embodiments of the present invention will be described in detail below. Example 1
[0024] Sodium aluminate and magnesium nitrate hexahydrate, with a magnesium-to-aluminum molar ratio of 0.5, were dissolved separately in 100 ml of deionized water and stirred until completely dissolved. The sodium aluminate solution was kept at 40 °C, while the magnesium nitrate hexahydrate solution was added dropwise at a controlled rate. After complete addition, the mixture was aged at 90 °C for 6 h. The mixture was then filtered, and the pH was washed to between 7 and 8. After drying and grinding, the catalyst precursor, magnesium-aluminum hydrotalcite, was obtained. This precursor was then directly calcined under a nitrogen atmosphere at a heating rate of 5 °C / min to 600 °C. The magnesium-aluminum composite oxide with a magnesium-aluminum ratio of 0.5 was obtained by maintaining the temperature at ℃ for 2 h. Example 2
[0025] Sodium aluminate and magnesium nitrate hexahydrate, with a magnesium-to-aluminum molar ratio of 0.5, were dissolved separately in 100 ml of deionized water and stirred until completely dissolved. The sodium aluminate solution was kept at 40 °C, and magnesium nitrate hexahydrate solution was added dropwise at a certain rate. After the addition was complete, the solution was aged at 90 °C for 6 h, filtered, and the pH was washed to between 7 and 8. The solution was then dried and ground to obtain the catalyst precursor magnesium aluminum hydrotalcite.
[0026] A certain mass of La(NO3)2∙6H2O was weighed to make La:Mg:Al = 1:9:18 and 1:1:5 (molar ratio), and dissolved in 100 ml of deionized water respectively. The magnesium aluminum hydrotalcite support was added to the above two solutions, stirred, and the support was fully impregnated and adsorbed with metal ions. Then, it was aged at 90 ℃ for 6 h, filtered, washed until neutral and dried for 12 h. Then, it was directly calcined under a nitrogen atmosphere at a heating rate of 5 ℃ / min to 600 ℃ and held for 2 h. After two impregnation, drying and calcination, lanthanum magnesium aluminum composite oxides with loadings of 12.72% and 55.18% were prepared. Example 3
[0027] Sodium aluminate and magnesium nitrate hexahydrate, with a magnesium-to-aluminum molar ratio of 0.5, were dissolved separately in 100 ml of deionized water and stirred until completely dissolved. The sodium aluminate solution was kept at 40 °C, and magnesium nitrate hexahydrate solution was added dropwise at a certain rate. After the addition was complete, the solution was aged at 90 °C for 6 h, filtered, and the pH was washed to between 7 and 8. The solution was then dried and ground to obtain the catalyst precursor magnesium aluminum hydrotalcite.
[0028] A certain mass of Ba(NO3)2 was weighed to make Ba:Mg:Al = 1:9:18 and 1:1:5 respectively, and dissolved in 100 ml of deionized water. The magnesium-aluminum hydrotalcite carrier was added to the above two solutions and stirred to fully impregnate the carrier and adsorb metal ions. Then, it was aged at 90 ℃ for 6 h, filtered, washed until neutral and dried for 12 h, and then directly calcined under a nitrogen atmosphere at a heating rate of 5 ℃ / min to 600 ℃ and held for 2 h. After two impregnation, drying and calcination, barium-magnesium-aluminum composite oxides with loadings of 11.97% and 51.94% were prepared. Example 4
[0029] Sodium aluminate and magnesium nitrate hexahydrate, with a magnesium-to-aluminum molar ratio of 0.5, were dissolved separately in 100 ml of deionized water and stirred until completely dissolved. The sodium aluminate solution was kept at 40 °C, and magnesium nitrate hexahydrate solution was added dropwise at a certain rate. After the addition was complete, the solution was aged at 90 °C for 6 h, filtered, and the pH was washed to between 7 and 8. The solution was then dried and ground to obtain the catalyst precursor magnesium aluminum hydrotalcite.
[0030] A certain mass of Mn(NO3)2 was weighed to make Mn:Mg:Al = 1:9:18 and 1:1:5 respectively, and dissolved in 100 ml of deionized water. The magnesium-aluminum hydrotalcite carrier was added to the above two solutions and stirred to fully impregnate the carrier and adsorb metal ions. Then, it was aged at 90 ℃ for 6 h, filtered, washed until neutral and dried for 12 h, and then directly calcined under a nitrogen atmosphere at a heating rate of 5 ℃ / min to 600 ℃ and held for 2 h. After two impregnation, drying and calcination, manganese-magnesium-aluminum composite oxides with loadings of 5.54% and 24.03% were prepared. Example 5
[0031] Sodium aluminate and magnesium nitrate hexahydrate, with a magnesium-to-aluminum molar ratio of 0.5, were dissolved separately in 100 ml of deionized water and stirred until completely dissolved. The sodium aluminate solution was kept at 40 °C, and magnesium nitrate hexahydrate solution was added dropwise at a certain rate. After the addition was complete, the solution was aged at 90 °C for 6 h, filtered, and the pH was washed to between 7 and 8. The solution was then dried and ground to obtain the catalyst precursor magnesium aluminum hydrotalcite.
[0032] A certain mass of Zr(NO3)4 was weighed to make Zr:Mg:Al ratios of 1:9:18 and 1:1:5, respectively, and dissolved in 100 ml of deionized water. The magnesium-aluminum hydrotalcite carrier was added to the above two solutions, stirred, and allowed to fully impregnate the carrier and adsorb metal ions. Then, it was aged at 90 °C for 6 h, filtered, washed until neutral and dried for 12 h, and then directly calcined under a nitrogen atmosphere at a heating rate of 5 °C / min to 600 °C and held for 2 h. After two impregnation, drying and calcination processes, manganese-magnesium-aluminum composite oxides with loadings of 9.62% and 41.47% were prepared.
[0033] The reaction conditions for the catalyst prepared in this invention are as follows: phenol / DMC = 1 / 2 (molar ratio), catalyst dosage: 0.4237 g (3% of the total mass of reactants), reaction temperature: 180 ℃, reaction pressure: atmospheric pressure, reaction time: 6 h, and rotation speed: 700 rpm.
[0034] Catalytic effect on phenol methylation:
[0035] SEM images ( Figure 1 The surface exhibits a porous / rough morphology (scale bar 1 μm, magnification 7500x), which is a typical characteristic of the composite oxide formed after calcination of magnesium aluminum hydrotalcite (the porous framework is formed after the layered structure of hydrotalcite collapses). The fine particles distributed on the surface (bright white area) are barium-based species that have been loaded. These particles were formed by calcination after adsorbing metal ions through an impregnation method.
[0036] The correlation between loading and particle distribution: This sample corresponds to a low loading of 11.97%: bright white particles are dispersed and small in size (when the loading is low, Ba species are uniformly dispersed on the support surface); the porous structure of the hydrotalcite support provides adsorption sites for Ba ions, and the impregnation-aging process allows Ba ions to be fully dispersed / enriched on the support surface; calcination at 600 ℃ under a nitrogen atmosphere: it not only maintains the porous framework of the support (avoiding excessive sintering), but also transforms Ba species into oxides and fixes them on the support surface, ultimately forming the morphology of "porous matrix + surface loaded particles" shown in the figure.
[0037] TEM images ( Figure 2 Its microscopic characteristics can be described in the following aspects (scale bar 10 nm, belonging to nanoscale observation): morphology and particle size: the image shows a nanoscale amorphous / microcrystalline aggregate, with an overall fine particle packing structure. The individual particle size is at the nanoscale, with no obvious large particle agglomeration, reflecting the material's "nanoscale dispersion." Phase characteristics: the image shows no clear crystal lattice fringes, indicating that the composite oxide may exist in an amorphous or microcrystalline state, which is consistent with the structural characteristics of composite oxides (amorphous / weakly crystalline) formed after calcination of hydrotalcite. The subtle differences in local brightness correspond to the differences in the compositional distribution of barium-based species and magnesium-aluminum oxide carriers (barium species are uniformly dispersed in the nanoparticles of the magnesium-aluminum matrix).
[0038] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.
Claims
1. A process for the preparation of a magnesium-aluminum composite oxide-based catalyst, characterized in that, The method comprises the following steps: (1) magnesium nitrate hexahydrate and sodium metaaluminate are respectively dissolved in deionized water and stirred until dissolved, the sodium metaaluminate aqueous solution is kept at a certain temperature during stirring, the magnesium nitrate hexahydrate solution is added dropwise, after completion, it is kept at a certain temperature for aging, then filtered, dried, and ground to obtain a catalyst precursor magnesium-aluminum hydrotalcite; (2) a metal salt solution with a certain molar concentration is prepared, the magnesium-aluminum hydrotalcite is immersed in the solution, heated and stirred in a water bath, and after several cycles of immersion, drying, and calcination, a magnesium-aluminum composite oxide-based catalyst is obtained; the metal salt contains at least one of lanthanum, barium, manganese, and zirconium metal salts.
2. The method of claim 1, wherein the magnesium-aluminum composite oxide-based catalyst is prepared by the steps of: (a) preparing a magnesium-aluminum composite oxide-based catalyst precursor; (b) adding a magnesium compound to the magnesium-aluminum composite oxide-based catalyst precursor; and (c) calcining the magnesium-aluminum composite oxide-based catalyst precursor. The sodium metaaluminate aqueous solution is kept at a temperature of 40 ℃.
3. The method of claim 1, wherein the magnesium-aluminum composite oxide-based catalyst is prepared by the steps of: (a) preparing a magnesium-aluminum composite oxide-based catalyst precursor; (b) calcining the magnesium-aluminum composite oxide-based catalyst precursor; and (c) reducing the calcined magnesium-aluminum composite oxide-based catalyst precursor. The aging temperature is 90 ℃, and the aging time is 6 h.
4. The method of claim 1, wherein the magnesium-aluminum composite oxide-based catalyst is prepared by the steps of: (a) preparing a magnesium-aluminum composite oxide-based catalyst precursor; (b) calcining the magnesium-aluminum composite oxide-based catalyst precursor; and (c) reducing the calcined magnesium-aluminum composite oxide-based catalyst precursor. The temperature of the water bath heating is 90 ℃, and the water bath heating time is 6 h.
5. The method of claim 1, wherein the magnesium-aluminum composite oxide-based catalyst is prepared by the steps of: (a) preparing a magnesium-aluminum composite oxide-based catalyst precursor; (b) calcining the magnesium-aluminum composite oxide-based catalyst precursor; and (c) reducing the calcined magnesium-aluminum composite oxide-based catalyst precursor. The calcination is performed under nitrogen atmosphere, the calcination temperature is 600 ℃, and the calcination time is 2 h.
6. The method of claim 1, wherein the magnesium-aluminum composite oxide-based catalyst is prepared by the steps of: (a) preparing a magnesium-aluminum composite oxide-based catalyst precursor; (b) calcining the magnesium-aluminum composite oxide-based catalyst precursor; and (c) reducing the calcined magnesium-aluminum composite oxide-based catalyst precursor. The lanthanum, barium, manganese, and zirconium metal salts are all nitrate salts.
7. The method of claim 1, wherein the magnesium-aluminum composite oxide-based catalyst is prepared by the steps of: (a) preparing a magnesium-aluminum composite oxide-based catalyst precursor; (b) calcining the magnesium-aluminum composite oxide-based catalyst precursor; and (c) reducing the calcined magnesium-aluminum composite oxide-based catalyst precursor. The molar ratio of metal ions in the metal salt to magnesium and aluminum is 1:1-9:5-18.
8. The application of the magnesium-aluminum composite oxide-based catalyst prepared by the method of any one of claims 1 to 7 in catalyzing the methylation reaction of phenol hydroxyl oxygen to generate anisole.
9. Use according to claim 8, characterized in that, The temperature of the methylation reaction to generate anisole is 180-200 ℃, and the reaction pressure is normal pressure.