Studies On The Catalytic Properties Of MOR-type And MFI-type Titanosilicates In Liquid-phase Selective Oxidation

Titanosilicate/H2O2 catalytic system for liquid-phase oxidation is the representa-tive figure of "Green Chemistry" for its mild reaction conditions, high utilization of atom, environmental friendliness, and the like. In this thesis, two kinds of titanosili-cate with MOR and MFI topology were used as the research objects; in response to the surface reaction process (chemical reaction, adsorption and desorption), diffusion process and transfer process in heterogeneous catalysis, a series of methods, the mod-ification of Ti active site and surface hydrophilicity/hydrophobicity, the modulation of crystal morphology and pore structure, and the introduction of a new reaction mode without co-solvent, were carried out, respectively, and the oxidation activity were en-hanced effectively.In the first part, the fluorine-implanted Ti-MOR (F-Ti-MOR) zeolites were suc-cessfully post-synthesized in liquid phase by using NH4F as the probe fluorine source, and the effects of solvent, NH4F amount, and fluorination temperature on the crystal structure and catalytic activity of thus obtained F-Ti-MOR zeolites were investigated in detail. Fluorination treatment leads to part loss of the tetrahedrally coordinated Ti species, but the electropositivity of the active Ti sites is increased benefited from the strong electron-withdrawing effects of SiO3/2F units generated during fluorination process, resulting in a tremendously enhanced oxidation capacity. Compared to water, methanol is much better for protecting the skeleton structure of Ti-MOR, implanting more fluorine, and generating more SiO3/2F units under harsh fluorination conditions (high NH4F amount, high fluorination temperature). F-Ti-MOR prepared under opti-mized fluorination conditions showed a cyclohexanone conversion of 99% in com-parison to only 30% conversion given by primitive Ti-MOR Fluorination treatment improves the surface hydrophobicity of Ti-MOR, which has no effect on the diffusion of inorganic small molecular, but the diffusion of organic molecules is presumed to be retarded by the doped-fluorine species inside the channels of Ti-MOR as a result of adsorption or interaction, which greatly decreases the activity of hydroxylation of aromatics. In addition, the fluorination treatment also introduces additional mesopores as the result of desilication, however, this effect has a very limited activity improve-ment for F-Ti-MOR.In the second part, a series of Ti-MOR zeolites with controllable crystal mor-phologies grown orientedly along the c-axis, that is, the running direction of the 12-membered ring main channels, were synthesized, and the effects of crystal mor-phology on its physicochemical properties and catalytic activity were investigated in detail. The mordenite zeolites with smaller crystals, especially consisting of nanopar-ticles, were in favor of deep dealumination, forming tetrahedrally coordinated Ti in TiCl4 vapor treatment. The physicochemical properties and catalytic activity of Ti-MOR exhibited regular changes with an increasing crystal length along the c-axis. The crystal length of ca.1 μm is a remarkable demarcation line governing the adsorp-tion properties and oxidation activity of Ti-MOR. Besides, the catalytic activity of Ti-MOR, which receives triple superimposition effects by dealumination, TiCl4 vapor treatment and reaction itself, behaves a linear dependence on the apparent diffusivity, for both ammoximation and hydroxylation. The hydroxylation of toluene is more sen-sitive than the ammoximation of cyclohexanone to the variety of crystal length for their different reaction paths.In the third part, hierarchical MOR (M-MOR) zeolites with intercrystalline mes-opores (4.3 nm) were hydrothermal synthesized by adding CTAB, and corresponding Ti-containing mordenite (M-Ti-MOR) catalysts were then prepared by a secondary isomorphous substation technique. The addition of CTAB decreases the crystallization rate. A part of CTAB molecules are located inside the channel of M-MOR, guiding M-MOR growing orientedly along the c-axis (12-MR main channels); and the other part CTAB micelles pile on the external surface, and supports between primary parti-cles, limiting the crystal growing along the a-axis, and generating intercrystalline mesopores after calcination. These mesopores has no effect on the diffusion of the substrates with large diameter (TiCl4, aromatics, etc.), but are in favor of small sub-strate molecules (acid, NH3, H2O2, etc.) diffusing into 12-MR through the 8-MR along b-axis. Because the 8-MR along b-axis is incoherence, the enhancement is very lim-ited. That is why the ammonia activity of M-Ti-MOR is just a little higher than con-ventional microporous Ti-MOR.In the fourth part, monodispersed amphiphilic zeolite/mesosilica composite ma-terial TS-1@KCC-1 (TK), which could stabilize Pickering emulsions for the ben-zene/H2O2 system, has been synthesized, and its physicochemical properties have been investigated in detail. Organic solvents are usually demanded for liquid-phase oxidation reactions to promote the catalytic activity. The Pickering interfacial cataly-sis (PIC) mode cannot only avoid this shortcoming, but also provide much larger in-terfacial surface areas than phase-boundary catalysis (PBC), which are in favor of ca-talysis by solving the external mass transfer limitation. The amphiphilic TK catalyst displayed a higher catalytic activity under PIC than PBC and conventional reaction conditions in the hydroxylation of benzene by hydrogen peroxide without co-solvent and under static conditions. Under optimized conditions, a TS-1@KCC-1 catalyst grafted with octyl chains (2.42 wt.%) could afford an interfacial activity of 1.1 mol (Ti-mol)-1. Moreover, PIC reaction conditions exhibited an excellent thermal stability and good reusability. But the activity of amphiphilic TK under PIC is rather low, re-sulted from the internal mass transfer limitation of TK.