Molecular Self-assembly Synthesis Of Novel Catalytic Materials And Their Applications In Green Chemistry

"Atom economy"is the core of"green chemistry"and can be achieved by employing high-performanced structuring catalysts. While the design, synthesis and application of catalysts have met the general requirements of most chemical reactions currently in chemical industry, it is still a far way to improve further the reactivities and properties of catalysts under the requirement of"green chemistry". The construction of high-performanced structuring catalysts is thus constitutes one of the most important hot-points and has been paid much attention from both academic and industrial domains all over the world. A high-performanced structural catalyst, as an advanced functionalized material, is characteristic of its unique architecture constructed with building blocks in certain regularity and specific properties regulated by its structure. As far as to the current technique, the high-performanced structural catalysts are mainly prepared via the molecular self-assembly route, which can generated ordered structures with an ordering in molecular or atomic levels, under weak interactions, such as, hydrogen bond, van der Waals forces and coulomb forces.. This dissertation was concentrated on the directional design of the high-performanced structural catalysts via molecular self-assembly, involving a few templates like nonionic surfactant, block copolymer, PAMAM dendrimers, ionic liquid and ice crystal as the templates. The performances of the prepared catalysts were evaluated by several selected reactions with industrial value.The dissertation focuses on the following five parts:1. The synthesis of transition metal-modified SBA-15 via supramolecular self-assembly.Transition metal-modified SBA-15 has been synthesized via supramolecular self-assembly of surfactants. Influencing factors, such as, the acidity of medium, the nature of surfactant and the batch composition, are investigated systematically. The specimens are characterized by means of XRD, TEM, DRS UV-Vis, BET, SEM, and NH₃-TPD. W-doped SBA-15 has been synthesized by in situ method, using aqueous H₃PO₄ or aqueous hydrochloric acid as acid medium, P123 as template, sodium tungstate and TEOS as tungsten and silicon resources, respectively. Comparing with those by using aqueous hydrochloric acid, the specimens synthesized in presence of H₃PO₄, have got some advantage such as ordered mesoporous channel, the content of W-doped and the acidity. In the synthesis system of M-SAB-15, using P123 and ionic surfactant as mixed template, the assembly forces between the inorganic and organic compounds are hydrogen bone and electrostatic interaction, which caused the stronger assembly between micelles and inorganic species and the as-synthesized specimens have owned more ordered structure. With CTAB adding, the tungsten in gel solution can be effectively incorporated into bone of SBA-15 and especially, the uniform morphologies of samples are obtained in presence of H3PO4. The additions of SDBS efficiently improve the crystallinity of Cr-SBA-15 and order pore channel.The catalytic properties of W-SBA-15 using H₃PO₄ as acid medium are first applied in the one-step selective oxidation reaction of oleic acid to azelaic acid, using aqueous hydrogen peroxide and O2 as oxidants. The yield and purity of azelaic acid is 43.6%, 96.7% while the molar ratio of W/Si in the gel is 0.025 and tungsten species in the mesoporous materials only with isolated [WO₄] tetrahedral.2. Synthesis of MnO_x nanotube template by nonionic surfactantMnOx nanotube with the wall being composed of monoclinic manganite, is first synthesized via a redox-assisted supramolecular assembly, using KMnO₄ and MnCl₂ as inorganic precusors, acetaldehyde an additive and polyoxyethylene (10) nonyl phenyl ether (TX-10) or polyoxyethylene fatty alcohol (AEO₉) as template. The samples are characterized by XRD, TEM, BET, XPS and Raman. The results of BET discuss that the walls of nanotube possess mesoporous pore. The parameters such as the molar ratio of reactants, temperature, and acetaldehyde are studied in details.3. Synthesis of Organic/inorganic composites template by PAMAM dendrimersA series of PAMAM, including different generations of PAMAM with ethylenediamine-core, generation 0.5².0 of PAMAM with hexanediamine-core and generation 0.5 of PAMAM with p-phenylenediamine-core, are successfully prepared by divergent synthesis and characterized by ESI-MS, 1H NMR, DTG-TG, FT-IR. Then, the PAMAM dendrimers are used as template to prepare the organic/inorganic composites.The morphologies of the lanthanum-contained organic/inorganic composites, using La(NO₃)₃ as inorganic precursor, can easy controlled by simply change the core of PAMAM. The nanorods are obtained template by the PAMAM with aliphatic diamine as core, while the catenular particles using aromatic diamine core. Bimetallic organic/inorganic composites, such as La-Co-EPAMAM, La-Cu-EPAMAM and La-Ag-PAMAM are synthesized by hydrothermal method using generation 1.0 PAMAM with ethylenediamine-core as template, La(NO₃)₃ , Co(NO₃)₂ , AgNO₃ and Cu(NO3)2 as inorganic precursor, respectively. The La-contained nanotubes are synthesized via hydrothermal method, using La(NO₃)₃ as La resource, EPAMAM-1.0 and AEO9 as mixed-templates. The textures of above specimens are tested by some technical measures, such as TEM, FT-IR and so on.The catalytic performances of the above organic/inorganic composites are tested in the oxidation reaction of cyclohexane with molecular oxygen. Compared with La2O3 powders, La-EPAMAM composites template by generation 1.0, 2.0 or 3.0 of PAMAM with ethylenediamine-core have better catalytic activities. The catalytic performances of La-EPAMAM are independent of generation of PAMAM and the conversions of cyclohexane, the selectivity of KA are about 7%, 94%.It is noteworthy that addition of Cu, Co, Ag can promote the activities of the catalysts. Using La-Co-EPAMAM, La-Cu-EPAMAM or La-Ag-PAMAM as catalysts, the conversion of cyclohexane are7.83%, 7.46%, 6.33% and the selectivity of KA are 98.4%, 96.4%, 94.5%。4. Synthesis of TS-1 zeolite using ionic liquid and TS-1 nuclei solution as co-templateThe influencing factors of synthesis of TS-1, such as kinds of ionic liquid, alkali source, temperature and mineralizer type, are studied in details. The specimens are characterized by XRD, FT-IR, SEM, TEM and BET. The results show that TS-1 zeolite synthesized under 140℃for 70h, using 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) and TS-1 nucleic solution as co-template, n-butyl amine as alkali source, F- as mineralizer, has higher crystallinity. Notably, TS-1 zeolites using EmimBF4 and TS-1 nucleic solution as co-template, HF as mineralizer and acid regulator, is first successfully prepared under weak acidic condition with the rod morphology. The results of XRD and DRS UV-Vis show that Titanium species in the TS-1 zeolites only with isolated [TiO₄] tetrahedral. Comparing with the traditional technology of TS-1, the new process is simplified for without distillation for removing ethanol and calcine for removing the organic template.As similar as commercial TS-1, TS-1 zeolites contained EmimBF4 have special activities in the reaction using dilute H2O2 as oxidant. The catalytic properties of the synthesized specimens are tested in the reaction of benzene with 30 wt% H2O2 to phenol, styrene with 30 wt% H₂O₂ to phenylacetaldehyde and benzaldehyde, respectively. The selectivity of phenol is 100% in the former reaction and the products only including phenylacetaldehyde and benzaldehyde in the latter.5. Green synthesis of porous materials using ice crystal as templateThe green synthesis of Si-Al oxide mesoporous materials and ZSM-5 zeolites are demonstrated. The Si-Al oxide mesoporous materials synthesized by using sodium silicate as Si resource, aluminum nitrate as Al resource, has BET 46.86 m2/g, pore volume 0.18cm3/g. ZSM-5 zeolites using Colloid silica and aluminum sulfate as inorganic precursor, has BET 168.9 m²/g, lower than ZSM-5 synthesized by organic template. The result of FT-IR indicates the molar Si/Al is lower than 25. The five-membered ring formed by ice crystal is similar to that of ZSM-5. Based on experimental results and phenomena, the mechanism of synthesis of ZSM-5 template by ice crystal is postulated.ZSM-5 synthesized by ice template is pretreated by the ionic exchanged method with NH₄NO₃ and then applied in the dehydration of ethanol to ethylene. The results show that the specimen (ice template) has the similar catalyst activity to the commercial HZSM-5.