CN104492491B - A kind of big ball Pd/Al of the films of ZIF 8 cladding grade2O3Egg-shell catalyst and preparation method thereof - Google Patents
A kind of big ball Pd/Al of the films of ZIF 8 cladding grade2O3Egg-shell catalyst and preparation method thereof Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims abstract description 63
- 238000002360 preparation method Methods 0.000 title claims description 18
- 238000005253 cladding Methods 0.000 title abstract 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 48
- 229910052593 corundum Inorganic materials 0.000 claims abstract description 48
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- 239000002105 nanoparticle Substances 0.000 claims abstract description 28
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- MFLKDEMTKSVIBK-UHFFFAOYSA-N zinc;2-methylimidazol-3-ide Chemical compound [Zn+2].CC1=NC=C[N-]1.CC1=NC=C[N-]1 MFLKDEMTKSVIBK-UHFFFAOYSA-N 0.000 claims description 43
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 22
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- 230000001939 inductive effect Effects 0.000 claims description 14
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 claims description 14
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- HLBBKKJFGFRGMU-UHFFFAOYSA-M sodium formate Chemical compound [Na+].[O-]C=O HLBBKKJFGFRGMU-UHFFFAOYSA-M 0.000 claims description 11
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- WYTZZXDRDKSJID-UHFFFAOYSA-N (3-aminopropyl)triethoxysilane Chemical compound CCO[Si](OCC)(OCC)CCCN WYTZZXDRDKSJID-UHFFFAOYSA-N 0.000 description 2
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- 229910003158 γ-Al2O3 Inorganic materials 0.000 description 2
- XIOUDVJTOYVRTB-UHFFFAOYSA-N 1-(1-adamantyl)-3-aminothiourea Chemical compound C1C(C2)CC3CC2CC1(NC(=S)NN)C3 XIOUDVJTOYVRTB-UHFFFAOYSA-N 0.000 description 1
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- JBFYUZGYRGXSFL-UHFFFAOYSA-N imidazolide Chemical compound C1=C[N-]C=N1 JBFYUZGYRGXSFL-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention provides a kind of big ball Pd/Al of the films of ZIF 8 cladding grade2O3Egg-shell catalyst, belongs to field of novel.The films of ZIF 8 coat Pd/Al2O3Pd/Al in eggshell catalyst2O3Core is with the spherical Al of grade2O3It is carrier, spherical Al2O3The particle diameter of carrier is 1 3mm；Loading type Pd/Al is prepared by infusion process2O3Catalyst, in loading type Pd/Al2O3Previously-introduced one layer of zinc oxide nano-particle layer, obtains the Pd/Al with zinc oxide nano-particle layer on catalyst2O3Carrier；Using zinc oxide nano-particle layer as the film eggshells of ZIF 8 layer and Pd/Al2O3The growth binding site of carrier, growth obtains the film eggshells of continuous ZIF 8 layer.Loaded noble metal catalyst is imparted to reactant and the high selectivity of product with the film eggshells of molecule screening function ZIF 8 layer.
Description
Technical Field
The invention belongs to the field of novel materials, and particularly relates to a ZIF-8 film-coated millimeter-sized large ball Pd/Al2O3An eggshell catalyst and a preparation method thereof.
Background
Noble metal catalysts have an extremely important position in oil refining, petrochemical industry and organic synthesis due to their non-replaceable catalytic activity and selectivity. Pd/Al2O3The catalyst has good hydrogenation activity as an industrial finished catalyst, and is widely applied to important industrial catalytic reactions of hydrogenation and oxidation reactions. However, there are major problems that the supported noble metal catalyst suffers from catalyst loss, agglomeration, sintering, poisoning, low selectivity, and the like. In recent years, the appearance and extensive research of the core-shell structure type nano metal catalyst formed by coating nano metal ions with organic polymers or inorganic oxides as shells indicate a direction for solving the problems of metal loss and poisoning resistance of the supported catalyst, and the supported nano metal catalyst has good research and application prospects.
Metal Organic Frameworks (MOFs) are porous crystalline materials that are self-assembled from Metal ions or Metal clusters and organic ligands by covalent or ion-covalent interactions. It has the outstanding advantages of high specific surface area, porosity, adjustable skeleton structure and the like, and has great application in the aspects of gas storage and separation, heterogeneous catalysis, molecular recognition, sensing and the likeAnd (4) potential. Zeolite Imidazolate Framework (ZIFs) is a class of MOFs widely studied, and has higher thermal stability and chemical resistance than other types of metal-organic frameworks. The topology of ZIF-8 is similar to that of a silicoaluminophosphate zeolite molecular sieve: the silicon-aluminum tetrahedron and the bridging oxygen atom are respectively replaced by metal ions and imidazole, and the pore size of the silicon-aluminum tetrahedron and the bridging oxygen atom is only allowed to be smaller than the kinetic diameterThe molecules of (2) are freely come in and go out, thereby having the characteristic of molecular sieving. ZIF-8 is adopted as a membrane material to coat the supported noble metal catalyst, so that the novel multifunctional core-shell catalyst with the functions of protecting core center active particles from aggregation, preventing poisoning and having shell shape selectivity can be obtained.
At present, the preparation method of the core-shell material taking ZIF-8 as the shell layer mainly comprises four methods: 1) surface modification of inert surface-containing core materials, e.g. of SiO2The particles are put into a solution of 3-Aminopropyltriethoxysilane (APTES), carboxyl groups are pre-modified on the surface of the particles, so that the growth of a ZIF-8 membrane is induced, and the obtained core-shell microspheres are used as a stationary phase of high performance liquid chromatography to obtain a high separation effect [ Fu YY, et al, chem-Eur J,2013,19(40):13484-13491.](ii) a 2) A layer assembly method is suitable for nuclear materials with rich surface charges, such as Ren et al, polyacrylic acid (PAA) nanoparticles are sequentially immersed in a methanol solution of zinc nitrate hexahydrate and 2-methylimidazole to obtain a ZIF-8 film, and the material has ultrahigh drug loading capacity and can be used for controlling and releasing drugs [ Ren H, et al. chem Common,2014,50(8): 1000-doped 1002.](ii) a 3) Secondary seeding, e.g. Sorribas et al, on mesoporous SiO2Growing ZIF-8 seed crystal on the surface, and putting the seed crystal into film forming liquid to obtain ZIF-8@ SiO2Core-shell materials [ Sorribas S, et al. chem Common,2012,48(75):9388-9390](ii) a 4) An in-situ synthesis method for preparing ZIF-8 film in situ from the core material with rich surface active functional groups, such as Lee, includes directly adding the polystyrene microspheres with rich carboxyl groups to the synthetic solution of ZIF-8, and passing throughVarying the number of film formations to adjust ZIF-8 film thickness and integrity [ Lee H J, et al. chem Common,2012,48(2):221-]. Although the ZIF-8-based core-shell material can be successfully synthesized by adopting the methods, the method can find that the method has higher requirements on the properties of the surface of the carrier or has more complicated required operation steps, not only consumes time and is complex, but also has single function of the prepared core-shell material, and does not relate to the application in the field of catalysis.
Disclosure of Invention
The invention aims to solve the technical problems of the existing supported noble metal catalyst and preparation of a ZIF-8 based core-shell material, and provides a novel supported noble metal core-shell catalyst with millimeter-scale size coated by a ZIF-8 film and a preparation method thereof. Mainly characterized by using a simple and effective unique preparation method, which is characterized in that firstly, the Al with the size of millimeter is used2O3The microsphere is taken as a carrier, and Pd nano-particles are loaded on the microsphere carrier to form Pd/Al2O3. Then Pd/Al2O3A ZnO nanoparticle layer is introduced to the surface of the egg core to serve as a ZIF-8 growth inducing layer, so that a continuous and uniform ZIF-8 membrane egg shell layer can be easily formed on the surface of the egg core, and the Pd/Al with high selectivity and millimeter-sized dimension is obtained2O3The @ ZIF-8 eggshell type catalyst is also helpful for solving the problems that the active center of the catalyst is easy to run off and the like, and is verified in the hydrogenation reaction.
The technical scheme of the invention is as follows:
ZIF-8 film-coated Pd/Al2O3The microsphere eggshell type catalyst is characterized in that spherical Al with the grain diameter of 1-3mm is selected2O3As a carrier, Pd ions are loaded by an ion exchange method and NaBH is used4Subjecting it to reduction of Pd0(ii) a Then in Pd/Al2O3Introducing a ZnO nanoparticle layer on the surface of the egg core as an induction layer formed by growth of a ZIF-8 membrane eggshell, and finally growing in a ZIF-8 synthetic solution to obtain a ZIF-8 membrane-coated Pd/Al2O3The microsphere with an eggshell structure. Coated with Pd/Al2O3The thickness of the ZIF-8 eggshell membrane of the egg core is 1-20 um.
ZIF-8 film-coated millimeter-sized large ball Pd/Al2O3Preparation method of eggshell type catalyst, and preparation method is used for obtaining supported Pd/Al2O3Catalyst, then in the supported Pd/Al2O3Introducing a zinc oxide nano particle layer into the catalyst in advance to obtain a carrier with the zinc oxide nano particle layer; the zinc oxide nano particle layer is used as a joint point of the ZIF-8 film and the carrier to obtain a continuous ZIF-8 film, thereby obtaining Pd/Al2O3@ ZIF-8 eggshell catalyst.
ZIF-8 film-coated millimeter-sized large ball Pd/Al2O3The preparation method of the eggshell type catalyst comprises the following specific steps:
(1)Pd/Al2O3preparation of the catalyst
0.079 g of PdCl are weighed out2Dissolved in 50 g of deionized water, and 0.96ml of 1mol/L HCl solution was added to the solution to prepare 8mmol/L H2PdCl4The solution was then weighed 8.6 grams of pretreated gamma-Al2O3Putting the carrier pellet into the solution, fully soaking, rotatably evaporating to dryness at a constant temperature of 333K, and then burning 823K in a muffle furnace for 6h under the condition that the temperature rise rate is 5K/min to obtain Pd/Al2O3A catalyst.
(2)Al2O3Preparation of ZnO nano particle induction layer introduced on microsphere
Preparing ZnO inducing layer by conventional sol-gel method, i.e. preparing zinc-containing sol solution, and soaking in Pd/Al2O3A zinc-containing glue layer is introduced on the surface of the pellet; drying at 80-120 ℃ for 0.5-3 h, and then roasting at 400 ℃ for 3h to obtain the Pd/Al coated with the ZnO nano particle inducing layer2O3A carrier;
(3) pretreatment of ZnO nanoparticle inducing layer
Pd/Al coated with the ZnO nanoparticle induction layer obtained in the step (2)2O3The carrier is put into 0.5 mol/L2-methylimidazolium alcohol solution, treated for 1 to 2 hours at 50 ℃, and then dried at 50 to 70 ℃ to obtain the pretreated ZnO/Pd/Al2O3A carrier;
(4) treating the treated ZnO/Pd/Al obtained in the step (3)2O3Placing the carrier in the prepared ZIF-8 film forming solution, injecting the solution into a stainless steel kettle containing a polytetrafluoroethylene lining, sealing the kettle, fixing the kettle in a rotary oven, rotating the kettle at the speed of 3-8r/min, controlling the reaction temperature to be 60-120 ℃, and carrying out solvothermal synthesis for 4-12 h to obtain ZIF-8 films with different thicknesses; the composition of the synthetic fluid is as follows: zinc chloride, 2-methylimidazole, sodium formate and methanol are used as raw materials of the film forming solution; wherein,
the molar ratio of the synthetic liquid is as follows:
Zn：2meIM：HCOONa：CH3OH ═ 1:1.5:0.15: 400. (methanol as solvent formulation)
Zn：2meIM：HCOONa：CH3CH2OH ═ 1:2:0.15:300 (ethanol as solvent formulation)
The invention solves the problems of more steps, higher synthesis temperature and overlong synthesis time of coating the ZIF-8 film outside the functional material, is beneficial to solving the problems of easy loss and poisoning of an active center and easy aggregation and sintering at high temperature of the traditional heterogeneous catalyst while endowing the catalyst with adjustable selectivity, and has wide application prospect.
Drawings
FIG. 1 shows Pd/Al2O3Surface SEM image of @ ZIF-8 eggshell catalyst.
FIG. 2 shows Pd/Al2O3Surface SEM image of @ ZIF-8 eggshell catalyst (FIG. 1, partially enlarged).
FIG. 3 shows Pd/Al2O3Cross-sectional SEM image of @ ZIF-8 eggshell catalyst.
FIG. 4 shows Pd/Al2O3XRD patterns of the @ ZIF-8 eggshell catalyst samples.
Detailed Description
The following detailed description of the invention refers to the accompanying drawings.
Example 1
(1)Pd/Al2O3Preparation of the catalyst
0.079 g of PdCl are weighed out2Dissolved in 50 g of deionized water, and 0.96ml of 1mol/L HCl solution was added to the solution to prepare 8mmol/L H2PdCl4Solution, then 8.6 g of pretreated Al is weighed2O3Putting the carrier pellet into the solution, fully soaking, rotatably evaporating to dryness at a constant temperature of 333K, and then burning 823K in a muffle furnace for 6h under the condition that the temperature rise rate is 5K/min to obtain Pd/Al2O3A catalyst.
(2)Al2O3Preparation of ZnO nano particle induction layer introduced on microsphere
The ZnO nano particle inducing layer is prepared by adopting a conventional sol-gel technology, namely, 0.5-2 mol/L of zinc-containing sol solution is prepared and then the dipping method is utilized to carry out Pd/Al on the zinc-containing sol solution2O3A zinc-containing glue layer is introduced on the surface of the pellet; drying at 80-120 ℃ for 0.5-3 h, and then roasting at 400 ℃ for 3h to obtain a ZnO nanoparticle inducing layer;
(3) pretreatment of ZnO nanoparticle inducing layer
Preparing 0.5 mol/L2-methylimidazole methanol solution, and reacting the ZnO/Pd/Al obtained in the step (2)2O3Pretreating carrier at 40-60 deg.C for 1-2 hr, and making strip at 50-70 deg.CDrying under the condition to obtain the pretreated ZnO/Pd/Al2O3A carrier;
(4) the pretreated ZnO/Pd/Al obtained in the step (3)2O3Placing the carrier in the prepared ZIF-8 film forming solution, injecting the solution into a stainless steel kettle containing a polytetrafluoroethylene lining, sealing the kettle, fixing the kettle in a rotary oven, rotating the kettle at the speed of 3-8r/min, controlling the reaction temperature to be 60-120 ℃, and carrying out solvothermal synthesis for 4-12 h to obtain ZIF-8 films with different thicknesses; the composition of the synthetic fluid is as follows: zinc chloride, 2-methylimidazole (2meIM), sodium formate and methanol are used as raw materials of the film-forming solution; wherein,
the molar ratio of the synthetic liquid is Zn to 2meIM to HCOONa: CH (CH)3OH＝1:1.5:0.15:400；
(5) Drying the catalyst obtained in the step (4) at the temperature of 50-70 ℃ to obtain Pd/Al2O3@ ZIF-8 eggshell catalyst.
(6) Respectively putting 0.3g of catalyst in a reaction device, adding 19ml of ethyl acetate, respectively adding 1ml of n-hexene, 0.8ml of cyclohexene and 0.5ml of cyclooctene into the reaction device, purging the reaction device for 3 times by adopting hydrogen, and reacting for 24 hours at 35 ℃. After the reaction, the results of the catalytic performance of the catalysts of the different samples were examined by gas chromatography (column: HP-5; FID) (Table 1). And respectively placing 0.3g of catalyst in the reaction device again, adding 19ml of ethyl acetate and 1ml of n-hexene, adding benzothiazole with different amounts, preparing the benzothiazole with the concentrations of 50ppm, 100ppm and 200ppm as poison molecules, purging the reaction device for 3 times by adopting hydrogen, and reacting for 24 hours at 35 ℃. After the reaction, the anti-poisoning effect of the catalyst was determined by gas chromatography (column: HP-5; FID) (Table 2).
Example 2
(1)Pd/Al2O3Preparation of the catalyst
0.079 g of PdCl are weighed out2Dissolved in 50 g of deionized water, 0.96ml of 1mol/L HCl solution was added to the solution to prepare 8mmol/L HCl solutionH2PdCl4Solution, then 8.6 g of pretreated Al is weighed2O3Putting the carrier pellet into the solution, fully soaking, rotatably evaporating to dryness at a constant temperature of 333K, and then burning 823K in a muffle furnace for 6h under the condition that the temperature rise rate is 5K/min to obtain Pd/Al2O3A catalyst.
(2) Respectively putting 0.3g of catalyst in a reaction device, adding 19ml of ethyl acetate, respectively adding 1ml of n-hexene, 0.8ml of cyclohexene and 0.5ml of cyclooctene into the reaction device, purging the reaction device for 3 times by adopting hydrogen, and reacting for 24 hours at 35 ℃. After the reaction, the results of the catalytic performance of the catalysts of the different samples were examined by gas chromatography (column: HP-5; FID) (Table 1). And respectively placing 0.3g of catalyst in the reaction device again, adding 19ml of ethyl acetate and 1ml of n-hexene, adding benzothiazole with different amounts, preparing the benzothiazole with the concentrations of 50ppm, 100ppm and 200ppm as poison molecules, purging the reaction device for 3 times by adopting hydrogen, and reacting for 24 hours at 35 ℃. After the reaction, the anti-poisoning effect of the catalyst was determined by gas chromatography (column: HP-5; FID) (Table 2).
Example 3
(1)Pd/Al2O3Preparation of the catalyst
0.079 g of PdCl are weighed out2Dissolved in 50 g of deionized water, and 0.96ml of 1mol/L HCl solution was added to the solution to prepare 8mmol/L H2PdCl4The solution was then weighed 8.6 grams of pretreated gamma-Al2O3Putting the carrier pellet into the solution, fully soaking, rotatably evaporating to dryness at a constant temperature of 333K, and then burning 823K in a muffle furnace for 6h under the condition that the temperature rise rate is 5K/min to obtain Pd/Al2O3A catalyst.
(2)Al2O3Preparation of ZnO nano particle induction layer introduced on microsphere
Prepared by the conventional sol-gel technologyPreparing a ZnO nano particle inducing layer, namely preparing 0.5-2 mol/L zinc-containing sol solution, and then performing a dipping method on Pd/Al2O3A zinc-containing glue layer is introduced on the surface of the pellet; drying at 80-120 ℃ for 0.5-3 h, and then roasting at 400 ℃ for 3h to obtain a ZnO nanoparticle inducing layer;
(3) pretreatment of ZnO nanoparticle inducing layer
Preparing 0.5 mol/L2-methylimidazole ethanol solution, and adding the ZnO/Pd/Al obtained in the step (2)2O3Pretreating the carrier for 1-2h at 40-60 ℃, and then drying at 50-70 ℃ to obtain the pretreated ZnO/Pd/Al2O3A carrier;
(4) the pretreated ZnO/Pd/Al obtained in the step (3)2O3Placing the carrier in the prepared ZIF-8 film forming solution, injecting the solution into a stainless steel kettle containing a polytetrafluoroethylene lining, sealing the kettle, fixing the kettle in a rotary oven, rotating the kettle at the speed of 3-8r/min, controlling the reaction temperature to be 60-120 ℃, and carrying out solvothermal synthesis for 4-12 h to obtain ZIF-8 films with different thicknesses; the composition of the synthetic fluid is as follows: zinc chloride, 2-methylimidazole (2meIM), sodium formate and ethanol are used as raw materials of the film-forming solution; wherein,
the molar ratio of the synthetic liquid is Zn to 2meIM to HCOONa: CH (CH)3CH2OH＝1:2:0.15:300；
(5) Drying the catalyst obtained in the step (4) at the temperature of 50-70 ℃ to obtain Pd/Al2O3@ ZIF-8 eggshell catalyst.
(6) Respectively putting 0.3g of catalyst in a reaction device, adding 19ml of ethyl acetate, respectively adding 1ml of n-hexene, 0.8ml of cyclohexene and 0.5ml of cyclooctene into the reaction device, purging the reaction device for 3 times by adopting hydrogen, and reacting for 24 hours at 35 ℃. After the reaction, the results of the catalytic performance of the catalysts of the different samples were examined by gas chromatography (column: HP-5; FID) (Table 1). And respectively placing 0.3g of catalyst in the reaction device again, adding 19ml of ethyl acetate and 1ml of n-hexene, adding benzothiazole with different amounts, preparing the benzothiazole with the concentrations of 50ppm, 100ppm and 200ppm as poison molecules, purging the reaction device for 3 times by adopting hydrogen, and reacting for 24 hours at 35 ℃. After the reaction, the anti-poisoning effect of the catalyst was determined by gas chromatography (column: HP-5; FID) (Table 2).
Table 1 shows the catalytic performance results of different samples.
TABLE 1
Table 2 shows the results of the anti-poisoning performance of the different samples.
TABLE 2
Claims (2)
1. ZIF-8 film-coated millimeter-sized large ball Pd/Al2O3The eggshell type catalyst is characterized in that the ZIF-8 film coats millimeter-sized large-ball Pd/Al2O3Pd/Al in eggshell catalyst2O3The core is spherical Al2O3As a carrier, spherical Al2O3The carrier has a particle diameter of 1-3mm and is loaded on spherical Al2O3Pd nano particles on the carrier are used as catalyst active centers; in Pd/Al2O3Introducing a ZnO layer on the surface of the core to serve as an induction layer for ZIF-8 film synthesis; bag (bag)Pd/Al coated with ZnO layer2O3The outer layer of the core is coated with a ZIF-8 film with a regular pore channel, namely the ZIF-8 film is coated with Pd/Al2O3The eggshell catalyst of (a); coated with Pd/Al2O3The core has a ZIF-8 film thickness of 1-20 um.
2. The ZIF-8 film-coated millimeter-sized macro-sphere Pd/Al of claim 12O3The preparation method of the eggshell type catalyst is characterized by comprising the following steps:
(1) introduction of ZnO nanoparticle inducing layer
The ZnO nanoparticle inducing layer is prepared by sol-gel method, i.e. zinc-containing sol solution is prepared first, and Pd/Al is added into millimeter-sized large spheres by dipping method2O3Introducing a zinc-containing glue layer on the surface; drying at 80-120 ℃ for 0.5-3 h, and then roasting at 400 ℃ for 3h to obtain the Pd/Al coated with the ZnO nano particle inducing layer2O3A carrier;
(2) Pd/Al coated by ZnO nano particle inducing layer2O3Pretreatment of the support
Pd/Al coated with the ZnO nanoparticle induction layer obtained in the step (1)2O3The carrier is put into 0.5 mol/L2-methylimidazolium alcohol solution, pretreated for 1-2h at 50 ℃, and dried at 50-70 ℃ to obtain the pretreated ZnO/Pd/Al2O3A carrier;
(3) the pretreated ZnO/Pd/Al obtained in the step (2)2O3Putting a carrier in a ZIF-8 film forming solution, putting the mixture in a stainless steel kettle containing a polytetrafluoroethylene lining, sealing, fixing in a rotary oven, rotating at the speed of 3-8r/min, and performing solvothermal synthesis for 4-12 h at the temperature of 60-120 ℃ to obtain ZIF-8 film-coated millimeter-sized nanosphere Pd/Al (Pd/Al) with different thicknesses2O3An eggshell catalyst;
the ZIF-8 film-forming solution comprises the following components: zinc chloride, 2-methylimidazole, sodium formate and methanol;
or zinc chloride, 2-methylimidazole, sodium formate and ethanol;
the mol ratio of each component in the ZIF-8 film-forming solution is as follows:
zinc chloride: 2-methylimidazole: sodium formate: methanol =1:1.5:0.15: 400;
zinc chloride: 2-methylimidazole: sodium formate: ethanol =1:2:0.15: 300.
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