New routes to hydrocarbon activation

24-P-06 - Study of coke and deactivation over H-Beta zeolite 

Shanghai Research Institute of Petrochemical Technology - China, zhuzhirong yahoo.com 

24-P-07 - Photoionization of N-alkylphenothiazines in transition-metal-ion modified mesoporous silica SBA-15 molecular sieves 

N-Alkylphenothiazines with variable alkyl chain lengths have been incorporated into mesoporous silica SBA-15 containing framework titanium or vanadium. Photoionization at room temperature forms stable alkylphenothiazine cation radicals (PCn+) which are monitored by electron spin resonance. The results reveal that the photoyield and stability of PCn increase with increasing titanium and vanadium content suggesting that these ions serve as effective electron acceptors. The overall photoyield and stability of PCn also increase with increasing alkyl chain length of the alkylphenothiazines. 

Miyazaki, S. Tsubaki, Y. Oumi and T. Uozumi 

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Apart from the development of aliphatic hydrocarbon soluble catalysts (Fig. 1) and the investigation of new preparative routes to catalyst precursors (Scheme ) extensive modelling studies are underway in an attempt to elucidate the active species and intermediates within the catalytic cycle. New approaches to supported catalysts via unusual organic support materials are also being developed. It is anticipated that these heterogeneous systems will provide in depth information on the operation of the CSIRO catalysts and the potential for extensive control over product distributions. 

The CH5 group, having a carbon atom in five-fold coordination, is called a carbonium ion. Carbonium-ion formation is an easier process in larger hydrocarbons, where the reaction is between the proton and the secondary or tertiary carbon atom, but is significantly more activated in the case of methane. The carbonium ion is the intermediate toward carbenium ions (3.29), where the positively charged carbon atom has a threefold coordination. Once formed, carbenium ions can be converted to hydrocarbons and new carbonium ions, in hydride transfer reactions, as in (3.31). Because of the lower activation energies of such reactions, the route via carbenium ions usually dominates over mechanisms involving carbonium ions. Reactions of the carbonium-ion type are terminated by a step in which a proton is transferred to the zeolite lattice. 

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