Titanium catalytic systems, study result

The study of ethylene and propylene copolymerisation, on vanadium and titanium catalysts of various compositions [70], led to the conclusion that studied catalytic systems contain two or three types of AC. This conclusion has been made as a result of the analysis of the MWD curves, carbon nuclear magnetic resonance spectroscopy analysis, and copolymers composition fractionation data. The analysis of a large number of copolymer fractions, produced by their dissolution in several solvents at various temperatures, has indicated the existence of several types of AC different both in stereospecificity and in reactivity. According to the authors of [70], a combination of copolymer fractionation results with gel chromatography data indicates the presence of two or three types of AC. 

The accessible product range is also broadened thanks to the exceptional intrinsic stereospecificity and molecular veight control of the catalytic system. High quality and consistency are favoured by easy and smooth control of the polymerization conditions due to the catalyst properties. In addition, future progress can be foreseen as a result of specialized development studies of this type of titanium trichloride catalyst currently under way. 

The overall catalytic cycle is believed to involve various titanium complexes which all have at least one isopropoxy ligand attached to the metal (Scheme 1). Given this fact, it is evident that kind and structure of the alkoxide can influence the catalysis, in particular the chirality transfer step (4—>5, via 2) and the displacement of the product sulfoxide from 5 to regenerate 3. Evidence for this assumption was obtained in studies with both other titanium alkoxides and alcohols such as methanol. In all cases less efficient catalyst systems resulted. 

Recent results in the field of catalytic oxidations with hydrogen peroxide are reviewed. Most effective catalysts fall into three categories metallorganic compounds, phase-transfer catalysts, redox zeolites. Metalloporphyrins and Pt-phosphine complexes are representative of first category. Mo and W polyoxome-talates and related systems, in association with phase transfer agents, belong to the second one. Titanium silicalite (TS-1) is the most studied redox zeolite. The oxidation of nitrogen and sulphur compounds and Fenton-like reactions are not reviewed. 

The synthesis of titanium silicalites TS-1 [10] and TS-2 [84-85], with MFI and MEL structure respectively, opened new opportunities in the oxidations with H O. TS-1 and TS-2, the former being the most studied, show similar properties in catalysis. Catalytic sites are isolated titanium atoms, incorporated into the zeolitic framework, in a channel system of about 0.55 nm average diameter [86-88], Different Ti-peroxo species, at lattice position, result from complex equilibria between TS-1, H O, and protic molecules [89-91],... 

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