CN114210362A - Preparation method and application of zinc ion modified Sn-Beta zeolite - Google Patents
Preparation method and application of zinc ion modified Sn-Beta zeolite Download PDFInfo
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Abstract
The invention belongs to the field of heterogeneous catalyst preparation, and relates to a preparation method and application of zinc ion modified Sn-Beta zeolite. The method mainly solves the problem that the residual hydroxyl nest of the Sn-Beta zeolite prepared by the post-synthesis method promotes the hydrolysis side reaction of caprolactone, skillfully utilizes the characteristic that zinc ions can be selectively combined with the hydroxyl nest, and accurately converts the residual hydroxyl nest into a weak Lewis acid site through simple zinc salt solution impregnation modification. Different from the prior method, the weak Lewis acid site with the zinc ion nature generated by the method has catalytic action on the main reaction of hydrogen peroxide and cyclohexanone to generate caprolactone, so that the modification of Sn-Beta zeolite by zinc ions can not only improve the product selectivity of the reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger to generate caprolactone, but also improve the conversion rate of the reaction under the condition of low solvent consumption.
Description
Technical Field
The invention belongs to the field of heterogeneous catalyst preparation, and relates to a preparation method of zinc ion modified Sn-Beta zeolite and application thereof in a reaction for synthesizing caprolactone through cyclohexanone oxidation.
Background
The silicon-aluminum Beta zeolite is a system with twelve-membered ring three-dimensional cross channelsThe framework of the high-silica-alumina ratio zeolite is formed by a tetragonal structure A and a monoclinic structure B, C along the [001 ]]Directionally bound to form a high silica zeolite having a high degree of stacking faults. The typical crystal morphology of Beta zeolite is an open octahedron with stronger structure
Acidity and higher hydrothermal stability. The characteristics enable the Beta zeolite to show excellent catalytic performance in alkylation, transalkylation, isomerization, cracking and other reactions.
The introduction of hetero atoms into Beta zeolite is an important method for expanding the catalytic application of Beta zeolite. The Sn-Beta zeolite is a complete Lewis acid type catalyst, and has unique catalytic action and wide potential application. There are two main methods for synthesizing Sn-Beta zeolite. The first method is a hydrothermal synthesis method, and is described in the publication Nature,2001,412 (6845): 423-425 reported the synthesis of this Sn-Beta zeolite. The method takes tetraethoxysilane as a silicon source, tin tetrachloride pentahydrate as a tin source, HF as a mineralizer and dealuminized Beta zeolite as seed crystal. The Sn-Beta zeolite with high crystallinity needs to be crystallized for 20 days at 140 ℃. The obtained Sn-Beta zeolite is applied to the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, the concentration of hydrogen peroxide solution is 35 wt%, 1, 4-dioxane is used as a solvent, and the solvent: ketone: h2O249.5: 1.5: 1, the reaction temperature is 90 ℃, and the reaction time is 3 hours, thereby obtaining the attractive results that the conversion rate of cyclohexanone is 52 percent and the selectivity of caprolactone is 98 percent. Chinese patent CN112897547A (application No. 2021-03-30) also discloses a similar synthesis method of Sn-Beta zeolite. The following patents and literature also relate to hydrothermal synthesis of Sn-Beta zeolite: CN102249258A (application date 2011-05-06), CN107244678A (application date 2017-07-04), CN107311201B (application date 2017-07-04), CN110422857A (application date 2019-07-25), CN110683557A (application date 2019-11-20), CN111285381A (application date 2020-03-09), CN112678842A (application date 2020-12-23), CN112645346A (application date 2020-12-23), CN112645347A (application date 2020-12-23), CN112551538A (application date 2020-12-23), CN112897547A (application date 2021-03-30)、ACS Sustainable Chemistry&Engineering, 2020,8, 9: 3796-: 425 + 426, Catalysts,2020,10 (11): 1249-: 17-24, Master thesis "Synthesis, characterization and catalytic MPVO reaction mechanism research of Sn-Beta molecular sieves", Lanzhou university (2016). The Sn-Beta zeolite prepared by the hydrothermal synthesis method is easy to regulate and control the Sn content in the zeolite. But has the disadvantages of overlong crystallization time, large fluoride consumption, serious environmental pollution and the like.
The second method is a post-synthesis method, which is based on the principle that the parent Al-Beta zeolite is subjected to acid dealumination treatment to obtain the all-silicon Beta zeolite with framework defect points, and then tin atoms are introduced into the framework defect points (hydroxyl pits) of the all-silicon Beta zeolite by different methods to form four-coordinated framework tin catalytic active sites. The post-synthesis method can introduce tin atoms into framework defect points of Beta zeolite by three methods, namely a gas-solid phase isomorphous substitution method, a liquid-solid phase isomorphous substitution method and a solid-solid phase isomorphous substitution method according to different tin sources. Publication The Journal of Physical Chemistry C,2011,115 (9): 3663-3670 is gas-solid phase isomorphous substitution. The tin source is gaseous anhydrous SnCl4The temperature of the gas-solid reaction was 500 ℃. The Sn-Beta zeolite obtained by gas-solid phase isomorphous substitution reaction on the basis of the dealuminized Beta zeolite is exposed in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, and has the main problems of low product selectivity and low catalytic activity. In the method, 50 wt% of hydrogen peroxide is used as an oxidant, acetonitrile is used as a solvent, and the ratio of the solvent: ketone: h2O2When the weight is 61: 2: 1, the conversion of cyclohexanone was 34.1% (theoretical conversion should be 50%) and the selectivity of caprolactone was 57.8% at a reaction temperature of 75 ℃ and a reaction time of 3 hours. It is known that in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide, the selectivity of the target product caprolactone is mainly influenced by the side reaction of hydrolysis ring opening of caprolactone to generate 6-hydroxycaproic acid. In the Sn-Beta zeolite prepared by post-synthesis, because the defect points of the framework of the all-silicon Beta zeolite are difficult to be completely isomorphously substituted by tin atoms, weak acid sites generated by hydroxyl pits of the defect points exist on the prepared framework of the Sn-Beta zeolite catalyst. Such weak acidsThe characteristic site catalysis caprolactone hydrolysis side reaction is an important reason for the low selectivity of the post-synthesis Sn-Beta zeolite catalyst to caprolactone.
Published Chinese Journal of Catalysis,2012,33 (5): 898-904 adopts liquid-solid phase isomorphous substitution method. The tin source is tin tetrachloride pentahydrate. The Sn-Beta zeolite obtained by liquid-solid isomorphous substitution reaction on the basis of the dealuminized Beta zeolite simultaneously exposes the problems of low reaction activity and low product selectivity in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide. For example, the catalyst is prepared by reacting cyclohexanone: h2O2: 1, 4-dioxane ═ 1: 1.4: 35 the cyclohexanone conversion and caprolactone selectivity were 23.6% (theoretical conversion should be 100%) and 70.0%, respectively. Compared with Sn-Beta zeolite prepared by a gas-solid phase isomorphous substitution method, the Sn-Beta zeolite prepared by the liquid-solid phase isomorphous substitution method contains more non-framework tin oxide species, so that the catalytic activity is lower.
U.S. Pat. No. 5,332,9621 (A1) (App. No. 2014-11-05) discloses a solid-solid phase isomorphous substitution process. The method is technically characterized in that concentrated nitric acid is firstly used for reacting with Beta zeolite to remove framework aluminum atoms. Then taking stannous acetate as a tin source, fully grinding and uniformly mixing the dealuminized Beta zeolite and the stannous acetate, and finally roasting at high temperature (550 ℃) to obtain the Sn-Beta zeolite. This Sn-Beta zeolite is obtained in the presence of cyclohexanone: h2O2: 1, 4-dioxane ═ 5: 1: 51, under the conditions that the reaction temperature is 95 ℃ and the reaction time is 4 hours, the conversion rate of cyclohexanone and the selectivity of caprolactone in the Baeyer-Villiger reaction of cyclohexanone and hydrogen peroxide are respectively 23.43 percent (the theoretical conversion rate is 20 percent) and 92 percent.
There is also a number of documents relating to the preparation of Sn-Beta zeolites by a post-synthesis process. For example, the synthesis of Sn-Beta zeolite by gas-solid isomorphous substitution is described in the following documents: CN110422857A (application No. 2019-07-25), The Journal of Physical Chemistry C,2011,115 (9): 3633 3670, Applied Catalysis A: general,2020,590: 117370, Master thesis "preparation and characterization of Al-Free Sn-Beta molecular sieve and performance research thereof in Beayer-Villiger catalytic oxidation", university of eastern Master (2011), Master thesis "gas-solid phase method synthesis, characterization and catalytic performance research of Sn-Beta zeolite", university of great courseware (2013), Master thesis "research of preparing Sn-Beta zeolite molecular sieve by isomorphous substitution method for catalyzing isomerization of glucose into fructose", university of great courseware (2013); the synthesis of Sn-Beta zeolite by liquid-solid isomorphous substitution is described in the following documents: green Chemistry,2013,15 (10): 2777-: 928- > 940, ACS Catalysis,2015,5 (2): 928-: 545-557; the following references relate to the synthesis of Sn-Beta zeolite by solid-solid isomorphous substitution: CN106984356A (application date 2017-05-05), ACS Catalysis,2014,4 (8): 2801-: 11736-11739, Master thesis "research on Rapid Synthesis of Sn-Beta molecular sieves and preparation of lactate by catalytic conversion of sugar", Zhengzhou university (2017).
The main advantage of the post-synthesis method compared to the hydrothermal synthesis method is that it does not involve the use of fluoride. Additionally, post-synthesis methods can, at least in theory, increase the framework tin content of Sn-Beta zeolites by utilizing the large number of framework defect points generated after dealumination of low silica to alumina ratio Beta zeolites. Of course, each post-synthesis method has a problem that, regardless of which method is used to introduce tin atoms into the framework defect sites of the all-silicon zeolite Beta, it is impossible to implant all the framework defect sites generated by dealumination with tetra-coordinated tin atoms. Thus, the sites of skeletal defects not implanted by tin atoms are present in the form of weakly acidic hydroxyl pits.
To our knowledge, few methods are currently available to solve the above-mentioned acidity problem of Sn-Beta zeolites. The solution provided in the Master thesis "study on preparation of lactate by catalytic conversion of glucose using Sn-Beta zeolite by improved post-treatment method", Zhengzhou university (2016) is to subject Sn-Beta zeolite prepared by solid-solid isomorphous substitution method to further hydrothermal modification treatment using tetraethylammonium hydroxide solution. During this modification treatment partial dissolution and recrystallization reactions of the Sn-Beta zeolite take place. During the process of partially dissolving the Sn-Beta zeolite by the TEAOH solution, one part of defect points are destroyed by dissolution reaction, and when the dissolved silicate species are subjected to recrystallization reaction on the Sn-Beta zeolite, the other part of defect points of the Sn-Beta zeolite are repaired. Therefore, the Sn-Beta modified in the way often contains mesopores, and becomes hierarchical-pore Sn-Beta zeolite. It is reported in the literature that the Sn-Beta zeolite modified by this method can significantly improve the yield of Methyl Lactate (MLA) in the glucose conversion reaction. At present, no research report of the Sn-Beta zeolite modified by the method for the reaction of the cyclohexanone and the hydrogen peroxide Beayer-Villiger is found, so the effect of the modification method on the reaction of the cyclohexanone and the hydrogen peroxide Beayer-Villiger is unknown.
Published Catalysis Science&Technology,2016,6, 2787-. The ion modification method involves Li+、Na+、K+、Cs+And NH4 +. The principle of the modification method is that alkaline cations are used for neutralizing and passivating weak acidic hydroxyl groups in Sn-Beta zeolite. It is reported in the literature that the Sn-Beta zeolite modified by the method has the weak B acidity of a hydroxyl pit passivated by the alkalinity of cations such as lithium, sodium, ammonium and the like, so that the hydrolysis side reaction of caprolactone in the Beayer-Villiger reaction of cyclohexanone and hydrogen peroxide is inhibited to a certain degree, and the selectivity of caprolactone is correspondingly improved.
Further, the publication ACS Omega 2021,6,284-293 provides a method for silylation modification of Sn-Beta. The silanization method comprises the following specific steps: the Sn-Beta zeolite prepared by post-synthesis method is mixed with a certain amount of silanization reagent by using absolute ethyl alcohol as solvent for modification treatment. The silanization reagents involved in the literature include mainly 3-Aminopropyltrimethoxysilane (APTMS), 3- (2-aminoethylamine) -propyltriethoxysilylamine (Detms). The principle of silanization modification is as follows: the silane species is grafted on the acid sites of Sn-Beta by utilizing the grafting reaction of a silanization reagent on the acid sites of Sn-Beta zeolite, and simultaneously the acid sites are covered. The modified Sn-Beta zeolite catalyst obtained by the modification method is applied to the reaction research of the scenedesmus for producing lactic acid in the literature. The result shows that the yield of the main product lactic acid of the Sn-Beta zeolite modified by 3-aminopropyl trimethoxy silicane (APTMS) is obviously improved. Under the optimal reaction conditions (190 ℃ and 5 hours), the yield of the lactic acid can reach 37 percent at most. Also, it is not known how the effect of silanization modification on improving the reaction performance of cyclohexanone and hydrogen peroxide of Sn-Beta zeolite can be achieved so far.
The invention patent CN108727180A (application date 2018-05-07) discloses an amination modification method of Sn-Beta zeolite. The method comprises the following steps: putting the Sn-Beta molecular sieve prepared by the post-synthesis method into absolute ethyl alcohol, adding an organic amine reagent into the absolute ethyl alcohol, and then treating the zeolite catalyst at the reflux temperature of the ethyl alcohol. It is clear that organic amines are basic molecules and are more reactive than silylating agents with weak acid sites in the Sn-Beta zeolite. The Sn-Beta zeolite modified by the method is used for sugar conversion reaction, and the target product is lactic acid.
The invention patent CN110575844A2 (application date 2019-08-16) discloses an alkaline earth metal modification method of Sn-Beta zeolite. Alkaline earth metal modification is also an effective method for eliminating the weak acid sites in Sn-Beta catalysts for Sn-Beta zeolites. The modification principle is similar to that of alkali metal ions. The Sn-Beta zeolite modified in this way is also used in sugar conversion reactions, the target product being lactic acid.
In summary, it can be seen that the existing modification methods for Sn-Beta zeolite prepared by post-synthesis methods are based on the elimination of the acidity of the residual hydroxyl pit, so as to achieve the purpose of inhibiting the catalytic action of the residual hydroxyl pit on the side reaction of caprolactone hydrolysis and ring opening, thereby leading caprolactone generated on Sn-Beta zeolite framework tin to become a final product. The above modification idea focuses only on improving the selectivity of the catalyst and thus does not lead to an improvement in the activity of the catalyst. In other words, the concept of the existing modification method is not to make the residual hydroxyl nest on the Sn-Beta zeolite useful, but simply to let it not play a side effect in the reaction.
We note that the all-silica zeolite Silicalite-1(S-1) is a crystalline silicate free of aluminium, and that the common S-1 zeolites (as synthesised hydrothermally in an alkaline medium) all contain some degree of framework defects, i.e. possess hydroxyl pits of different forms, and that these also have a weakly acidic nature. S-1 zeolite is favored because of its weakly acidic hydroxyl nest. Since it has been found that the weak acidity of the hydroxyl nest of the deficient S-1 zeolite is very suitable for catalyzing the Beckmann rearrangement reaction of cyclohexanone oxime. In the gas phase reaction at about 350 ℃, cyclohexanone oxime can be catalyzed by weak acidic hydroxyl pit of defective S-1 zeolite to generate caprolactam product with high efficiency. This fact is helpful to understand the authenticity and severity of the harmfulness of the residual hydroxyl pits in the Sn-Beta zeolite of the present invention. Since caprolactam is a monomer for producing nylon-6. Thus, a number of researchers have conducted extensive developmental studies around the hydroxyl nest in S-1 zeolites. It is worth mentioning that the publications RSC Advances,2018, 8: 18663 18671 in studying the zinc nitrate impregnation modification of defective S-1 zeolites, it was found that zinc ion species readily bind to the hydroxyl nest of defective S-1 zeolites, creating Lewis acid sites. The Lewis acid site can obviously catalyze the reaction of dehydrogenating isobutane to generate isobutene.
Furthermore, we have also noted that HZSM-5 zeolite synthesized by a different method (which belongs to the MFI crystal structure as S-1 zeolite but contains aluminum atoms in the framework. framework aluminum atoms give rise to strongly acidic Bronsted acid sites) also contains framework silicon defects to a different extent. According to the publications Catalysts,2019, 9: 100, the deficient HZSM-5 zeolite also exhibits weak acidity associated with the hydroxyl nest due to the presence of a considerable number of hydroxyl nests therein. That is, on defective ZSM-5 zeolites, there are both strong bronsted acid sites associated with framework aluminum and weak bronsted acid sites associated with hydroxyl pit defect sites. Of particular note, the doctor's paper "study of the characterization, modification and catalytic properties of deficient ZSM-5 zeolites", university of technology (2021) has shown that silicon defects (silicon hydroxyl pits) on ZSM-5 zeolites are also particularly susceptible to binding by zinc ion species. This study revealed the surprising fact that: even in the presence of strong bronsted acid sites, the zinc ion species preferentially bind to the weakly acidic hydroxyl crypts of the ZSM-5 zeolite, thereby converting the weak bronsted acid sites of the hydroxyl crypts to weak lewis acid sites. This conclusion is valid for the introduction of zinc ions into deficient ZSM-5 zeolites, whether by impregnation with zinc nitrate solution or by chemical liquid deposition of diethyl zinc. The results also show that the weak Lewis acid site converted from the hydroxyl nest of the defective ZSM-5 zeolite can form a concerted catalytic action with the inherent strong Bronsted acid site of the zeolite, and the conversion rate of the raw material and the selectivity of an aromatic hydrocarbon product and a useful precursor (olefin) thereof are improved in the propane aromatization reaction.
Disclosure of Invention
The invention aims to provide a preparation method of zinc ion modified Sn-Beta zeolite and a method for improving selectivity of caprolactone which is a product in oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger under low solvent consumption by using the zinc ion modified Sn-Beta zeolite. The invention has the remarkable characteristics that: the Sn-Beta zeolite prepared by a synthesis method after the impregnation modification of a salt solution of zinc ions. In the modification, zinc ions can be selectively and preferentially combined with the residual hydroxyl pits in the Sn-Beta zeolite, so that the residual hydroxyl pits are accurately converted into weak Lewis acid sites. According to research, weak Lewis acid sites formed by zinc ions in the residual hydroxyl pits of the Sn-Beta zeolite have a catalytic effect on promoting the main reaction of hydrogen peroxide and cyclohexanone to generate caprolactone. Therefore, the modified Sn-Beta catalyst prepared by the method not only can improve the selectivity of the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger to generate caprolactone products, but also can improve the conversion rate of the reaction.
In addition, through research, the use amount of dioxane (also called dioxane) solvent has great influence on the selectivity of the product caprolactone for producing the caprolactone by the Beayer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone. Increasing the amount of solvent can be accomplished by reducing the water concentration (generally, H of hydrogen peroxide feedstock)2O2The concentration is 30-70 wt.%, and the rest is water. In addition to carrying in water, H2O2An equimolar amount of water is also produced after the oxidant is reacted) to reduce the chance of caprolactone coming into contact with water and undergoing hydrolytic ring-opening side reactions. As such, the published and technical literature teaches the selection of the product caprolactone in the oxidation of cyclohexanone and hydrogen peroxide by the prepared and/or modified Sn-Beta zeolite (either hydrothermal or post-synthesis) in the presence of a large amount of dioxane solventAnd (4) sex. For example, in the prior art, the molar ratio of the reactants of dioxane and cyclohexanone as solvents is at most close to 50: 1 or higher, at least as high as 35: 1. it will be appreciated that the use of large amounts of dioxane solvent will mask the acidity problem of the catalyst. But too high solvent usage is not at all suitable for industrial applications. We find that the post-synthesis Sn-Beta zeolite catalyst modified and prepared by the method can inhibit the hydrolysis side reaction of caprolactone under the condition of low solvent consumption, thereby improving the selectivity of caprolactone.
The technical scheme adopted by the invention is as follows:
a preparation method of zinc ion modified Sn-Beta zeolite comprises the following specific steps:
the first step is as follows: preparation of dealuminated zeolite Beta precursor
In principle, any desired silica to alumina ratio precursor zeolite Beta can be used to prepare the dealuminated zeolite Beta precursor. The precursor Beta zeolite with any silicon-aluminum ratio can be a common Beta zeolite product which is sold in the market or synthesized by the common knowledge. Considering that the precursor Beta zeolite with lower silicon-aluminum ratio can generate more framework defect sites after being completely dealuminated, more tin atoms can be allowed to enter the framework of the all-silicon Beta zeolite and generate more Lewis acid type active centers in the post-synthesis, and the Sn-Beta zeolite catalyst is undoubtedly beneficial to preparing the high-activity hydrogen peroxide and cyclohexanone Beayer-Villiger oxidation reaction catalyst, the invention recommends that the precursor Beta zeolite raw material with low silicon-aluminum ratio is properly selected when preparing the dealuminated Beta zeolite precursor. In particular, the present invention recommends the use of a silica to alumina molar ratio (SiO)2/Al2O3) The precursor Beta zeolite raw material is between 20 and 100, and the silicon-aluminum molar ratio (SiO) is preferably used2/Al2O3) Between 25 and 60 precursor zeolite Beta starting material.
The precursor zeolite Beta feedstock may be dealuminated by any method reported in the literature. For example, common high-temperature steam dealumination, dealumination by complexing agents such as EDTA, dealumination by organic acid and inorganic acid solutions, or dealumination by a combination of different methods. The invention has no limit to the dealumination method of the precursor Beta zeolite raw material,only the silica to alumina mole ratio (SiO) of the resulting dealuminated zeolite Beta precursor is required2/Al2O3) Not less than 700, preferably not less than 800, more preferably not less than 900.
In view of the advantages of low cost, simple process and high efficiency of dealuminating a precursor zeolite Beta feedstock with solutions of inorganic acids such as hydrochloric acid and nitric acid, it is suggested that dealuminating a precursor zeolite Beta feedstock with solutions of hydrochloric acid and nitric acid may be considered preferable for the preparation of an acceptable dealuminated zeolite Beta precursor, with conditional resolution of spent acid issues. The acid dealumination of zeolite Beta is described in the following patents and literature: chemical Communications,1998, 1: 87-88, Microporous and Mesoporous Materials,1999, 31: 163- & ltSUB & gt 173, & ltSUB & gt Catalysis letters,2009,130 (3): 655 663, Materials Chemistry and Physics,2002, 78: 551-557, Catalysis letters,2009,130 (3): 655 663, Microporous and Mesoporous Materials,2012,163: 122-130, ACS Catalysis,2014,4 (8): 2801-2810, Journal of CO Utilization,2020, 36: 54-63.
Generally speaking, dealuminated zeolite Beta precursors meeting the requirements of the present invention are readily prepared when the hydrochloric acid solution has a concentration of up to 6M or when the nitric acid has a concentration of up to 8-15M. The acid dealumination to produce dealuminated zeolite Beta precursors from precursor zeolite Beta starting materials can be accomplished by engineers familiar with the art based on their own experience or by reference to zeolite Beta dealumination procedures reported in published literature and patents. For example, the precursor zeolite Beta feedstock can be fully dealuminated according to the following general knowledge procedure: firstly, putting a precursor Beta zeolite raw material in a temperature environment of 80-200 ℃ for full drying, and roasting at a high temperature of not less than 500 ℃ for a time of not less than 3h, thereby ensuring that no organic matter (usually template molecules) exists in the pore channels of the Beta zeolite. In the process, an 8-15M nitric acid solution is prepared. Then, according to the liquid-solid ratio of 50: 1-10: 1(ml/g) the dried parent zeolite Beta was mixed with nitric acid solution and refluxed at a temperature of 70-100 c for 10-30 h. Finally, the dealuminized Beta zeolite matrix is obtained by conventional solid-liquid separation, washing of the solid product with water (until the washing liquid is neutral), drying and roasting.
Silicon-aluminum ratio (SiO) of precursor Beta zeolite raw material2/Al2O3) The measurement can be carried out by X-ray fluorescence spectroscopy (XRF); the dealuminated zeolite Beta precursors generally have very low aluminum content and thus have a very low silica to alumina ratio (SiO)2/Al2O3) The measurement requires inductively coupled plasma emission spectroscopy (ICP), atomic absorption spectroscopy (AA), or the like.
The second step is that: preparing Sn-Beta zeolite on dealuminized Beta zeolite matrix by adopting post-synthesis method
The tin atoms are introduced into framework defect points of a matrix of the dealuminized Beta zeolite to form four-coordinated framework tin catalytic active sites, and the four-coordinated framework tin catalytic active sites can be prepared by adopting three modes of gas-solid phase isomorphous substitution, liquid-solid phase isomorphous substitution and solid-solid phase isomorphous substitution according to different tin sources. The present invention recommends the use of solid-solid isomorphous substitution. Tin atoms are introduced into framework defect points of a dealuminized Beta zeolite matrix through a solid-solid phase isomorphous substitution technical route to form four-coordinated framework tin catalytic active sites, and various solid tin compounds can be adopted as precursors of the tin atoms, such as tin tetrachloride pentahydrate, stannous chloride dihydrate and tin acetate. It is stated, however, that the present invention is not limited to specific tin sources and technical routes for the post-synthesis preparation of Sn-Beta zeolites. The solid-solid isomorphous substitution method is recommended because the technical route is simple, can use various tin sources, has low production cost and can meet the basic requirements of low non-framework tin content and high framework tin content in the Sn-Beta zeolite. In particular, the present invention suggests that the Sn-Beta zeolite prepared by post-synthesis has a silicon to tin molar ratio (Si/Sn) below 100, preferably below 70, more preferably below 40.
The Sn-Beta zeolite can be prepared by engineers familiar with the art based on their own experience or by reference to isomorphous substitution methods, particularly solid-solid isomorphous substitution methods, reported in published literature and patents. For example, the following patents and documents refer to isomorphously substituting hydroxyl pit defect sites on dealuminated Beta zeolite matrix with tin atoms to prepare Sn-Beta zeolite with low non-framework tin content and high framework tin content: US2016279621(a1) (application date 2014-11-05), CN106984356A (application date 2017-05-05), ACS Catalysis,2014,4 (8): 2801-: 11736-11739, Master thesis "research on Rapid Synthesis of Sn-Beta molecular sieves and preparation of lactate by catalytic conversion of sugar", Zhengzhou university (2017). The following is an example of a solid-solid isomorphous substitution process for the preparation of Sn-Beta zeolite: firstly, the amount of the tin compound precursor to be added can be calculated according to the amount of the dealuminated Beta zeolite matrix and the number of defect sites on the framework (equivalent to the number of the removed aluminum atoms); then, fully grinding and mixing the fully dried dealuminized Beta zeolite parent body with a metered stannide precursor; and finally, putting the fully mixed molecular sieve and stannide precursor mixture into a high-temperature furnace, and roasting for 5-15 hours at the temperature of 400-650 ℃ to obtain the Sn-Beta zeolite catalyst.
The third step: zinc ion modification treatment of Sn-Beta zeolite catalyst
The Sn-Beta zeolite prepared by post-synthesis can be modified by dipping with a solution of zinc salt to obtain the zinc ion modified Sn-Beta zeolite catalyst. The impregnation method is a conventional method for preparing heterogeneous catalysts, and is widely adopted due to the advantages of simple process, stable and easily-mastered technology, strong adaptability, low requirements on production equipment conditions, low processing cost and the like. Impregnation methods can be divided into equal volume impregnation (i.e. dry impregnation, meaning that the volume of the impregnating solution is used in an amount comparable to the pore volume of the impregnated solid) and excess liquid impregnation (meaning that the volume of the impregnating solution is used in an amount greater than the pore volume of the impregnated solid). The present invention is not limited to equal volume impregnation or excess liquid impregnation. However, it is required to ensure that all of the Sn-Beta zeolite solid is impregnated with the zinc ion solution when the equivalent-volume impregnation method is used, especially in the case where the Sn-Beta zeolite is a formed catalyst. In the case of excess liquid impregnation, it is desirable to remove the free liquid by filtration, blow-drying, etc. after impregnation to ensure adequate drainage of the liquid from the solids. It is not desirable to remove excess water from the impregnate by steam drying, otherwise it is difficult to produce a modified catalyst having a uniform zinc ion content. It is even less desirable to wash the impregnate with deionized water. The water washing operation is generally used in the process of preparing modified zeolite catalysts by ion exchange methods. The invention does not suggest implanting zinc ions into the Sn-Beta zeolite by an ion exchange method. Because the interaction of zinc ions with the hydroxyl nest is not a strong interaction between ion pairs, but a weak interaction between zinc ions and silicon hydroxyl groups. Water washing can result in loss of zinc ions from the hydroxyl nest.
In principle, water soluble zinc salts can be used for the zinc ion impregnation modification described in the present invention. However, zinc salts such as zinc nitrate and zinc acetate, in which the anion is easily volatilized or decomposed after firing, are recommended. When zinc salts such as zinc phosphate and zinc sulfate are used, retention of phosphate and sulfate, which are difficult to decompose, and clogging of catalyst channels are avoided. Of course, when zinc sulfate is used as the source of zinc ions, the sulfate can be removed by final hydrogenation.
When zinc ion impregnation modification of Sn-Beta zeolite with a suitable zinc salt is performed, it is important to strictly control the amount of zinc salt. Obviously, when the amount of the zinc salt is low, the residual hydroxyl pit in the Sn-Beta zeolite cannot be converted into the Lewis acid site as much as possible; on the other hand, when the amount of the zinc salt is too large, it is inevitable that too much zinc ions remain in the pores of the Sn-Beta zeolite. The excessive zinc ions can become guest-sub-nanometer ZnO particles in Sn-Beta zeolite pore channels during roasting treatment, and the blocking can be caused to the zeolite pore channels. Theoretically, the number of residual hydroxyl pit defects in the Sn-Beta zeolite can be determined by firstly measuring a hydroxyl infrared spectrogram of a sample by a Fourier transform infrared spectrometer and then determining by a semi-quantitative method. In practice, infrared spectrum characterization and trial and error with varying amounts of zinc salt may be combined to determine the appropriate amount of zinc salt. In the zinc ion modified Sn-Beta zeolite catalyst with proper zinc salt dosage, the infrared characteristic band (3400) -3600cm of hydroxyl pit defect-1) Should substantially disappear. Meanwhile, the moderately modified zeolite catalyst has a modification effect of simultaneously improving the product selectivity and the raw material conversion rate in the reaction of producing caprolactone by oxidizing hydrogen peroxide and cyclohexanone Beayer-Villiger.
The zinc ion impregnation modification treatment of the Sn-Beta zeolite can be carried out by engineers familiar with the art according to their own experience or by referring to the methods reported in the prior publications and patents. The following documents all relate to a method for zinc ion impregnation of modified zeolites: molecular Catalysis,2019, 70: 112, 119, Industrial Engineering Chemistry Research,2020,59 (37): 16146-: 14674-14687, Catal Lett,2021, you: 955 amongst others, 955 overhead 965, natural gas chemistry (C1 chemistry and chemistry), 2021,46 (03): 48-52+99, Master thesis 'Zinc modified ZSM-5 molecular sieve catalysis methanol to aromatics', university of continental project (2019), Master thesis 'study of Zinc modified ZSM-5 for methanol to aromatics reaction', university of continental project (2020). Specific examples of impregnation of modified Sn-Beta zeolite with zinc salt solutions are given below: firstly, according to the total amount of Sn-Beta zeolite prepared by a post-synthesis method to be treated and the number of hydroxyl pits (hydroxyl pits not occupied by a tin compound precursor) of the Sn-Beta zeolite determined by an infrared spectroscopy method, estimating the zinc salt dosage and carrying out experimental impregnation modification, and simultaneously checking the disappearance condition of the residual hydroxyl pits of the Sn-Beta zeolite sample subjected to the impregnation modification by different metered zinc salt solutions by using an infrared spectrum to select the proper zinc salt dosage; then, fully mixing the fully dried Sn-Beta zeolite with a metered zinc salt solution, and stirring and soaking for a certain time at a certain water bath temperature. And carrying out suction filtration, draining, drying overnight and high-temperature roasting on the impregnated sample to obtain the Zn-Sn-Beta zeolite catalyst. Among them, zinc salts are preferably zinc nitrate and zinc acetate; the concentration of the zinc salt solution is preferably dilute, and the recommended range is between 0.01 and 0.3M, and preferably between 0.05 and 0.15M; the ratio (liquid-solid ratio) of the volume (ml) of the zinc salt solution to the weight (g) of the Sn-Beta zeolite is not less than 1: 1, preferably not less than 3: 1; the dipping temperature can be selected from 60-90 ℃, preferably 60-80 ℃; the impregnation time can be selected from 0.5-10h, preferably 1-3 h. After the zinc-modified catalyst has drained the aqueous solution, it may be dried overnight at 50-200 deg.C, preferably 80-110 deg.C; the dried modified catalyst can be calcined at 400-600 ℃ for 3-6 h. Preferably at 450-550 ℃ for 3-6 hours.
Of course, in addition to the zinc salt solution impregnation method, zinc powder reduction method and titration method of organic zinc such as diethyl zinc can be used to modify the residual hydroxyl pit defect sites of the Sn-Beta zeolite and generate weak Lewis acid sites. These methods are characterized by the quantification of the silicon hydroxyl groups in the hydroxyl nest as compared to zinc salt solutionsAnd (4) reacting. For example, the reaction formula of zinc powder and silicon hydroxyl is: zn +2SiOH ═ (SiO)2Zn+H2. However, the modification process using zinc powder or diethyl zinc is complex, the equipment requirement is high, the modification condition is harsh, and the industrialization difficulty is large. For example, diethyl zinc is very reactive and needs to be handled under anhydrous conditions, which can lead to risks such as fire and even explosion when exposed to water. The following documents refer to the zinc powder modification of zeolite catalysts: doctor paper "conversion studies of isobutane on modified nano HZSM-5 catalysts", university of college graduate (2013), doctor paper "studies of characterization, modification and catalytic properties of deficient ZSM-5 zeolites", university of college graduate (2021). The following documents refer to the process of diethyl zinc modified zeolites: catalysis,2019, 9: 100. engineers familiar with the art and having sufficient experience with zinc dust and diethyl zinc modified zeolite catalysts can, at best, experience themselves in zinc ion modification of Sn-Beta zeolite using both methods. And will not be described in detail.
The zinc ion modified Sn-Beta zeolite prepared by the method is used as a full Lewis type solid acid catalyst for catalyzing the oxidation reaction of Beayer-Villiger to synthesize caprolactone, and specifically comprises the following steps:
the modified Sn-Beta catalyst prepared by the method not only can improve the product selectivity of the reaction of oxidizing hydrogen peroxide and cyclohexanone Beayer-Villiger to generate caprolactone, but also can improve the conversion rate of the reaction.
For the reaction of producing caprolactone by oxidizing hydrogen peroxide and cyclohexanone Beayer-Villiger, the selectivity of the product caprolactone is greatly influenced by the dosage of dioxane (also called dioxane) solvent. However, the post-synthesis Sn-Beta zeolite catalyst modified by the method of the invention can be prepared under the condition of very low solvent dosage, for example, the molar ratio of the reactants of solvent dioxane and cyclohexanone is 10: 1-2: 1, the hydrolysis side reaction of the caprolactone is inhibited, thereby improving the selectivity of the caprolactone. The basic method for using the modified Sn-Beta zeolite catalyst in the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger is as follows: and evaluating the Beayer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone by adopting an intermittent kettle type reaction device. First, to a reaction deviceAdding a solvent 1, 4-dioxane, a reactant cyclohexanone and a metered hydrogen peroxide solution in sequence, then adding a certain amount of zinc ion modified Sn-Beta zeolite catalyst, heating and stirring for catalytic reaction. Wherein the mass concentration range of the hydrogen peroxide raw material solution is 30-50 wt%; the raw material proportion should satisfy the following requirements: 1, 4-dioxane: cyclohexanone: h2O2(2-10): 1: (0.2-2), and the dosage of the catalyst is 0.05-0.25g/g cyclohexanone.
The effect of the invention can be evaluated by the conversion rate of the raw material (cyclohexanone) and the selectivity of the product (caprolactone) in the Beayer-Villiger oxidation reaction of hydrogen peroxide and cyclohexanone. The resultant liquid reaction mixture was analyzed by gas chromatography model 2014C, and the column model was OV-1101(30 m. times.0.32 mm. times.0.5. mu.m). The column temperature was 80 deg.C, the detector was 250 deg.C, the injection port temperature was 250 deg.C, and the temperature was programmed. The conversion rate of cyclohexanone is quantitatively calculated by adopting an external standard method, and the selectivity of caprolactone is calculated by adopting an area normalization method.
The invention has the beneficial effects that:
(1) the zinc ion modified Sn-Beta zeolite prepared by the method is used as a catalyst, so that the selectivity of the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger to generate caprolactone products can be improved, and the conversion rate of the reaction can be improved.
(2) The zinc ion modified Sn-Beta zeolite prepared by the method is used as a catalyst, and can inhibit the hydrolysis side reaction of caprolactone under the condition of low solvent consumption, so that the selectivity of caprolactone is improved.
(3) The method can be used for modifying Sn-Beta synthesized by a direct hydrothermal method, and can also be used for modifying corresponding Ti-Beta zeolite and other zeolites containing Sn and Ti.
Drawings
FIG. 1 shows the hydroxyl group vibration IR spectra before and after dealumination of zeolite Beta and before and after modification of Sn-zeolite Beta in example 1.
Detailed Description
The present invention is further illustrated by the following examples, but the present invention is not limited to these examples.
Example 1: this example illustrates that after the Sn-Beta zeolite catalyst prepared by the post-synthesis method is modified by zinc ion impregnation, residual hydroxyl pits disappear, and the cyclohexanone conversion rate and caprolactone selectivity of the modified catalyst in the Baeyer-Villiger oxidation reaction of cyclohexanone and hydrogen peroxide are improved.
The first step is as follows: preparation of dealuminated zeolite Beta precursor
(1) With a commercially available silicon to aluminum ratio (SiO)2/Al2O3) Preparing a dealuminated zeolite Beta precursor for the precursor zeolite Beta raw material of 25;
(2) firstly, the silicon-aluminum ratio (SiO)2/Al2O3) The precursor Beta zeolite raw material of 25 is dried at 120 ℃ overnight and then calcined at 550 ℃ for 3h to completely remove the organic matter in the pore channels.
Note that: in carrying out this step, if it is found that no black smoke is emitted during the firing of the sample, or the sample after firing shows complete white color, it indicates that no organic matter is present in the sample. And recovering the sample for later use.
However, if black smoke is emitted during the roasting process and the sample still appears black, gray or yellow after 3 hours, it indicates that the organic matter (mainly the template) in the sample has not been completely removed. Therefore, the baking time should be properly extended until the sample is completely whitened;
(3) preparing 13M nitric acid solution. Then stirring according to the liquid-solid ratio of 20: 1(ml/g) ratio 20g of dried Si/Al ratio (SiO)2/Al2O3) The precursor zeolite Beta starting material, 25, was added to a three-necked flask containing 400ml of a 13M nitric acid solution. The batch was then heated to 100 ℃ with stirring and the batch was subjected to continuous acid dealumination treatment with stirring at this temperature for 20 h. During this time, the three-necked flask was kept under reflux. After the dealuminization reaction is carried out for 20 hours, the feed liquid is cooled and filtered to recover a solid product. The solid product was then washed repeatedly with deionized water to neutrality, and then dried (110 ℃ C. overnight) and calcined (550 ℃ C., 3h) to produce a dealuminated zeolite Beta precursor. The silicon-aluminum ratio (SiO) of the dealuminized Beta zeolite matrix was measured by ICP method2/Al2O3) Is 980.
The second step is that: preparing Sn-Beta zeolite on dealuminized Beta zeolite matrix by adopting post-synthesis method
(1) Preparing Sn-Beta zeolite on the basis of a dealuminated Beta zeolite matrix by using stannous chloride dihydrate as a tin source and adopting a solid-solid isomorphous substitution method;
(2) the amount of stannous chloride dihydrate was calculated to be about 1.25g based on the amount of dealuminated Beta zeolite precursor and the number of defect sites on the framework (equivalent to the number of aluminum atoms removed) using 10g of dealuminated Beta zeolite precursor. Fully grinding and uniformly mixing metered stannous chloride dihydrate and metered dealuminized Beta zeolite matrix;
(3) the mixture of milled and uniformly mixed stannous chloride dihydrate and dealuminized Beta zeolite matrix is put into a quartz tube in a horizontal high-temperature roasting furnace, the temperature is raised to 550 ℃ at the heating rate of 10 ℃/min, and then the mixture is roasted for 6 hours at 550 ℃ for carrying out solid-solid phase isomorphous substitution reaction. During this period, nitrogen was first purged with a gas flow of 60mL/min for 3 hours, and then with air for 3 hours under the same gas flow. After finishing the solid-solid isomorphous substitution reaction, collecting the Sn-Beta zeolite product for later use.
(4) The Si/Sn ratio composition of the Sn-Beta zeolite product was determined by XRF and showed that a Sn-Beta zeolite with Si/Sn ═ 20 was obtained. The hydroxyl bands of the sample were characterized by Fourier transform infrared spectroscopy, and the results are shown by Sn-Beta lines in FIG. 1. It can be seen from the hydroxyl infrared spectrum that there are still some residual framework defect sites in the prepared Si/Sn ═ 20 Sn-Beta zeolite which are not isomorphously substituted by tin atoms.
The third step: zinc ion modification treatment of Sn-Beta zeolite catalyst
(1) Using zinc nitrate water solution as impregnation liquid, and carrying out zinc ion modification treatment on Sn-Beta zeolite with Si/Sn being 20 by adopting an excess impregnation method;
(2) in order to determine the appropriate concentration of the zinc nitrate impregnation solution, 3400-3600cm in a hydroxyl infrared spectrogram of an Sn-Beta zeolite sample with Si/Sn ═ 20 is firstly subjected-1The bands were semi-quantitatively analyzed for the estimation of residual hydroxyl pit defect number. On the basis, the liquid-solid ratio is 4: 1(ml/g) in the early stage, the zinc nitrate concentration of the trial test was determinedThe degree ranges between 0.01 and 0.3M. According to the change condition of the hydroxyl infrared spectrum of the modified sample obtained by the test, the proper concentration of the zinc nitrate impregnating solution is determined to be 0.15M;
(3) a sample of 2.5 gSi/Sn-20 Sn-Beta zeolite was added to 10ml of a 0.15M zinc nitrate solution with stirring. Then carrying out 2h excess impregnation treatment on the Sn-Beta zeolite catalyst at the water bath temperature of 60 ℃;
(4) after the impregnation treatment, the modified solid catalyst was recovered by centrifugal separation, and the wet catalyst was placed in the air to drain the water. When no droplets are drained off for a long time, the wet catalyst solids can be transferred to a 110 ℃ oven for overnight drying. Then, roasting the dried modified sample for 6 hours at 540 ℃ by using a muffle furnace to obtain the Sn-Beta zeolite (Zn-Sn-Beta-1) modified by zinc ions;
(5) the modified catalyst is characterized by infrared spectrum of hydroxyl, and the infrared spectrum of the hydroxyl is shown as Zn-Sn-Beta-1 line in figure 1. From the spectrum, the Zn-Sn-Beta-1 catalyst sample is shown in the specification of 3400--1The bands in between indicate that the hydroxyl pits have substantially disappeared. This indicates that zinc ions have occupied residual hydroxyl nest defect sites of the Sn-Beta zeolite catalyst by the impregnation modification treatment.
The fourth step: and catalyzing the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger by using a zinc ion modified Sn-Beta zeolite catalyst to synthesize caprolactone.
(1) A250 mL round bottom flask was used as a reactor, and the reaction was carried out according to the following 1, 4-dioxane: cyclohexanone: h2O2The molar ratio is 4: 2: 1 in the proportion of 1. Firstly, adding 4.11g of 1, 4-dioxane as a solvent into a reactor, then adding 1.96g of cyclohexanone, 0.5g of modified Sn-Beta zeolite (Zn-Sn-Beta-1) and 0.68g of 50 wt% hydrogen peroxide, putting the mixture into a rotor, and receiving condensed water; (2) the stirring was turned on and the oil bath temperature was set to 60 ℃ and heating was started. And starting timing after the reactor reaches the specified reaction temperature, and setting the reaction time to be 2 h.
(3) After the reaction, the reaction solution was centrifuged, and the supernatant was collected and subjected to gas chromatography. According to the chromatographic analysis data, the reaction result is calculated as follows: cyclohexanone conversion 27.75% (theoretical conversion 50%) and selectivity to product caprolactone 93.80%.
Comparative example 1: this comparative example is used to illustrate that if the Sn-Beta zeolite catalyst prepared by post-synthesis is directly used in the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger without being modified by zinc ion impregnation, the conversion of cyclohexanone is reduced and the selectivity of caprolactone is also reduced.
Example 1 was repeated, but the Sn-Beta zeolite catalyst prepared in the second step was used directly in the fourth step of the Beayer-Villiger oxidation of hydrogen peroxide and cyclohexanone without the third step of the zinc ion modification treatment. The reaction result became 22.36% cyclohexanone conversion and 91.73% product selectivity. Compared with the example 1, the Sn-Beta zeolite catalyst prepared by zinc ion impregnation modification can improve the conversion rate of cyclohexanone and the selectivity of caprolactone.
Comparative example 2: this comparative example is provided to illustrate, for example, the use of a low concentration nitric acid to silicon to aluminum ratio (SiO)2/Al2O3) If the precursor Beta zeolite raw material of 25 is subjected to insufficient dealumination treatment, and the dealumination degree is far lower than the minimum requirement (not lower than 700) of the invention on the silicon-aluminum ratio of the dealuminated Beta zeolite precursor, the zinc ion modified catalyst cannot achieve the expected modification effect.
Example 1 was repeated, but in the first step, a 0.7M nitric acid solution to silicon to aluminum ratio (SiO)2/Al2O3) When the precursor Beta zeolite raw material of 25 is subjected to dealumination treatment, the silicon-aluminum ratio of the dealumination Beta zeolite precursor can only reach 180. In the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger, the conversion rate of cyclohexanone is only 10.36 percent, and the selectivity of products is 91.03 percent. This comparative example 1 demonstrates that when the dealumination degree of the dealuminated zeolite Beta precursor is insufficient, the modified catalyst has fewer reactive sites associated with tin and zinc, which is not favorable for increasing the conversion of cyclohexanone. Comparative example 3: this comparative example is intended to illustrate that the use of a large amount of solvent in the B-V oxidation of hydrogen peroxide and cyclohexanone is beneficial to the conversion and conversion of cyclohexanoneThe selectivity of the lactone is improved. However, the use of an excessive amount of solvent is obviously disadvantageous for industrialization.
Example 1 was repeated, but in the evaluation of the Beayer-Villiger oxidation reaction, the reaction was evaluated according to the following 1, 4-dioxane: cyclohexanone: h2O2The molar ratio is 40: 2: 1 in the proportion of 1. The reaction result was 24.43% cyclohexanone conversion and 93.89% product selectivity. As can be seen from comparison of the results of the reaction carried out in example 1, a high solvent content is advantageous in increasing the conversion of cyclohexanone and the selectivity to caprolactone. However, under the condition of high solvent consumption, the concentration of the product in the reaction solution is very low, the energy consumption for separating the product is very large, and the requirement of double-carbon economic target is not met, so that the method is not beneficial to industrialization.
Comparative example 4: this comparative example is intended to illustrate that, for example, in the B-V oxidation reaction of hydrogen peroxide and cyclohexanone, the amount of solvent used is large, which is advantageous to the improvement of the conversion rate of cyclohexanone and the selectivity of caprolactone. The same good reaction results were achieved even without zinc ion modification of the Sn-Beta zeolite catalyst. That is, the use of a large amount of solvent causes a problem of poor selectivity of the masking catalyst. The problem of poor catalyst selectivity will be revealed in the industrial production, because the reaction mode with too large amount of solvent is impossible.
Example 1 was repeated, but on the one hand the Sn-Beta zeolite catalyst prepared in the second step was used directly in the fourth step for the Beayer-Villiger oxidation of hydrogen peroxide and cyclohexanone without being subjected to the third step of zinc ion modification, and on the other hand, when evaluated in terms of 1, 4-dioxane: cyclohexanone: h2O2The molar ratio is 40: 2: 1 in the proportion of 1. The reaction result was cyclohexanone conversion 23.96% and product selectivity 94.45%.
Example 2: this example illustrates that the concentration of zinc nitrate impregnation solution is an important factor affecting the effect of zinc ion impregnation of modified Sn-Beta zeolite catalyst.
Example 1 is repeated, but when the zinc ion impregnation modification in the third step is carried out, the concentrations of zinc nitrate solution are changed to 0.05M and 0.3M in sequence, the cyclohexanone conversion rates of the Zn-Sn-Beta zeolite catalyst obtained after the modification in the oxidation reaction of hydrogen peroxide and cyclohexanone Beayer-Villiger are respectively 25.47% and 24.23%, and the selectivity of caprolactone products is respectively 93.44% and 96.68%.
Example 3: this example illustrates that the temperature of the zinc ion impregnation modification is an important factor affecting the effectiveness of the zinc ion impregnation modified Sn-Beta zeolite catalyst.
Example 1 was repeated, but when the third step of zinc ion impregnation modification was carried out, the impregnation temperature was changed to 40 ℃, 80 ℃ and 90 ℃ in this order, and the modified Zn-Sn-Beta zeolite catalyst was used in the oxidation reaction of hydrogen peroxide and cyclohexanone B-V, the cyclohexanone conversion rates were 23.63%, 24.68% and 21.68%, respectively, and the caprolactone product selectivities were 93.50%, 96.41% and 94.35%, respectively. From the comparison with example 1, it can be seen that the best effect is obtained when the zinc ion impregnation modification temperature is 60 ℃.
Example 4: this example illustrates that the liquid-solid ratio of the zinc salt solution to the Sn-Beta zeolite catalyst is an important factor affecting the effect of the zinc ion-impregnated modified catalyst when the zinc ion-impregnated modification is performed.
Example 1 was repeated, but when the third step of zinc ion impregnation modification was carried out, the liquid-solid ratio (ml/g) of the zinc salt solution to the Sn-Beta zeolite catalyst was changed to 10: 1 and 20: 1, when the modified Zn-Sn-Beta zeolite catalyst is used for the B-V oxidation reaction of hydrogen peroxide and cyclohexanone, the conversion rates of the cyclohexanone are respectively 19.08 percent and 22.96 percent, and the selectivity of caprolactone products is respectively 95.79 percent and 96.24 percent. From the comparison with example 1, it can be seen that the liquid-to-solid ratio of the zinc salt solution to the Sn-Beta zeolite catalyst is 4: 1, the effect is best.
Example 5: this example illustrates that the time for zinc ion impregnation modification is an important factor in the effect of zinc ion impregnation modification of Sn-Beta zeolite catalyst.
Example 1 was repeated, but when the third step of zinc ion impregnation modification was carried out, the impregnation modification time was changed to 1h and 3h in this order, and when the modified Zn-Sn-Beta zeolite catalyst was used in the oxidation reaction of hydrogen peroxide and cyclohexanone B-V, the cyclohexanone conversion was 22.55% and 24.20%, respectively, and the caprolactone product selectivity was 92.68% and 92.91%, respectively. From the comparison with example 1, it can be seen that the best effect is obtained when the zinc ion impregnation modification time is 2 hours.
Claims (10)
1. A preparation method of zinc ion modified Sn-Beta zeolite is characterized by comprising the following specific steps:
the first step is as follows: preparation of dealuminated zeolite Beta precursor
By using SiO2/Al2O3The calculated silica-alumina molar ratio is between 20 and 100, and the silica-alumina molar ratio of the precursor Beta zeolite is not less than 700;
the second step is that: preparing Sn-Beta zeolite on dealuminized Beta zeolite matrix by adopting post-synthesis method
Introducing tin atoms to framework defect points of a matrix of the dealuminized Beta zeolite to form four-coordinated framework tin catalytic active sites, and performing gas-solid phase isomorphous substitution, liquid-solid phase isomorphous substitution or solid-solid phase isomorphous substitution according to different tin sources; the silicon-tin molar ratio of the prepared Sn-Beta zeolite is lower than 100;
the third step: zinc ion modification treatment of Sn-Beta zeolite catalyst
The Sn-Beta zeolite prepared by post-synthesis is impregnated and modified by adopting a zinc salt solution to obtain a zinc ion modified Sn-Beta zeolite catalyst; the impregnation method includes equal-volume impregnation and excess liquid impregnation.
2. The process of claim 1, wherein in the first step, SiO is used for modification of Sn-Beta zeolite2/Al2O3Precursor Beta zeolite raw material with the calculated silica-alumina molar ratio of 25-60; the resulting dealuminated zeolite Beta precursor has a silica to alumina mole ratio of no less than 800.
3. The method for preparing the zinc ion modified Sn-Beta zeolite according to claim 1 or 2, characterized in that in the first step, a precursor Beta zeolite raw material is subjected to dealumination treatment by using a solution of hydrochloric acid or nitric acid to prepare an qualified dealuminated Beta zeolite precursor; and the concentration of the hydrochloric acid solution is required to reach 6M, or the concentration of the nitric acid is required to reach 8-15M.
4. The method for preparing the zinc ion modified Sn-Beta zeolite of claim 3, wherein the dealumination treatment of the precursor Beta zeolite raw material by using a nitric acid solution is as follows:
firstly, putting a precursor Beta zeolite raw material in a temperature environment of 80-200 ℃ for drying, and roasting at a high temperature of not less than 500 ℃ for a time of not less than 3h, thereby ensuring that no organic matter exists in a pore channel of the Beta zeolite; using 8-15M nitric acid solution, and mixing according to the liquid-solid ratio of 50: 1-10: mixing dried parent Beta zeolite with nitric acid solution at the ratio of 1ml/g, and refluxing for 10-30h at the temperature of 70-100 ℃; and finally, carrying out solid-liquid separation, washing the solid product with water until the washing liquid is neutral, drying and roasting to obtain the dealuminized Beta zeolite matrix.
5. The process according to claim 1, 2 or 4, wherein the Zn ion-modified Sn-Beta zeolite is,
in the second step, when the solid-solid isomorphous substitution method is adopted to prepare the Sn-Beta zeolite, the specific steps are as follows:
firstly, measuring and calculating the amount of a tin compound precursor to be added according to the amount of a dealuminated Beta zeolite matrix and the number of defect sites on a framework of the dealuminated Beta zeolite matrix;
then, fully grinding and mixing the dried dealuminized Beta zeolite parent body with a metered stannide precursor; and finally, placing the mixed molecular sieve and stannide precursor mixture into a high-temperature furnace, and roasting for 5-15 hours at the temperature of 400-650 ℃ to obtain the Sn-Beta zeolite catalyst.
6. The method for preparing the zinc ion modified Sn-Beta zeolite of claim 3,
in the second step, when the solid-solid isomorphous substitution method is adopted to prepare the Sn-Beta zeolite, the specific steps are as follows:
firstly, measuring and calculating the amount of a tin compound precursor to be added according to the amount of a dealuminated Beta zeolite matrix and the number of defect sites on a framework of the dealuminated Beta zeolite matrix; then, fully grinding and mixing the dried dealuminized Beta zeolite parent body with a metered stannide precursor; and finally, placing the mixed molecular sieve and stannide precursor mixture into a high-temperature furnace, and roasting for 5-15 hours at the temperature of 400-650 ℃ to obtain the Sn-Beta zeolite catalyst.
7. The process according to claim 1, 2, 4 or 6, wherein the Sn-Beta zeolite is modified with zinc ions,
in the third step, when excess liquid is adopted for impregnation, the specific steps are as follows:
firstly, according to the total amount of Sn-Beta zeolite prepared by a post-synthesis method and the hydroxyl nest number of Sn-Beta zeolite measured by an infrared spectroscopy method, estimating the zinc salt dosage and carrying out experimental impregnation modification, and simultaneously checking the disappearance condition of residual hydroxyl nests of Sn-Beta zeolite samples which are subjected to the impregnation modification by different metering zinc salt solutions by using an infrared spectrum to select the proper dosage of zinc salt; then, fully mixing the fully dried Sn-Beta zeolite with a metered zinc salt solution, and stirring and dipping in a water bath; carrying out suction filtration, draining, drying overnight and high-temperature roasting on the impregnated sample to obtain the Zn-Sn-Beta zeolite catalyst;
wherein the zinc salt is zinc nitrate or zinc acetate; the concentration of the zinc salt solution is between 0.01 and 0.3M; the ratio of the volume of the zinc salt solution to the weight of the Sn-Beta zeolite is not less than 1: 1 ml/g; the dipping temperature is between 60 and 90 ℃; the dipping time is 0.5-10 h; after the zinc modified catalyst drains off the water solution, drying at 50-200 ℃ overnight; the dried modified catalyst is calcined at the temperature of 400-600 ℃ for 3-6 h.
8. The method for preparing Sn-Beta zeolite of claim 1, 2, 4 or 6, wherein in the third step, zinc powder reduction or diethyl zinc organozinc titration is used to modify the residual hydroxyl pit defect sites of Sn-Beta zeolite and generate weak Lewis acid sites.
9. The zinc ion modified Sn-Beta zeolite prepared by the preparation method of claims 1-8 is used as a full Lewis type solid acid catalyst.
10. The use according to claim 9 for the catalytic synthesis of caprolactone by oxidation with Beayer-Villiger, in particular as follows:
firstly, sequentially adding a solvent 1, 4-dioxane, a reactant cyclohexanone and a metered hydrogen peroxide solution into a reaction device, then adding a zinc ion modified Sn-Beta zeolite catalyst, heating and stirring for catalytic reaction; wherein the mass concentration range of the hydrogen peroxide solution is 30-50 wt%; the raw material proportion should satisfy the following requirements: 1, 4-dioxane: cyclohexanone: h2O2(2-10): 1: (0.2-2), and the dosage of the catalyst is 0.05-0.25g/g cyclohexanone.
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