Browsing by Author "Chuang, T. T."

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Catalytic activity and selectivity of NaOH-doped γ-aluminas: Dehydration and dehydrogenation of 3-pentanol
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (4), 1972) Chuang, T. T.; Lana, I. G. Dalla
The catalytic activity of the γ-alumina surface has been investigated using infra-red spectroscopy and interpreted in terms of strong and weak Brønsted-acid sites and Lewis-acid sites. Doping of the γ-alumina with NaOH was used to eliminate Brønsted-acid sites. The influence of the two types of sites upon catalytic activity and selectivity was shown with studies of the simultaneous dehydration and dehydrogenation of 3-pentanol on pure γ-alumina or on several doped aluminas of varying NaOH content. Although the fractional activity of the weak Brønsted-acid sites is greater than that for the Lewis-acid sites, the differences in catalytic behaviour are considerably larger and are attributed to reduced accessibility of the Lewis-acid sites. The selectivity exhibited towards the two reactions was shifted from dehydration to dehydrogenation by eliminating Brønsted-acid sites.
CO2 Poisoning of the ^'-Alumina-catalyzed Reaction of COS with SO2
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (3), 1973) Chuang, T. T.; Lana, I. G. Dalla; Liu, C. L.
The isomerization reaction of 3,3-dimcthylbut-l-cnc (1), to produce 2,3-dimcthylbut-l-cnc (11) and 2,3-dimethylbut-2-cne (111), has been investigated over a series of copper-exchanged X-type zeolites. The reaction is believed to proceed via carbonium ion intermediates and the ability of the copper zeolites to exhibit acidic-type behaviour was demonstrated. The results emphasized the important role that the copper cations play in the reaction, and the intermediate formation of a hydrocarbon copper complex was postulated. The observed poisoning effect of water was explained in terms of the preferential formation of a copper-aqua complex. The isomerization of II was shown to be a more facile process. The exchange reactions of I and II, with deuterium oxide and deuterium, were examined over one of the copper-containing zeolites. Substantial exchange was only observed under conditions where isomerization also took place. With deuterium oxide, the exchange of I was multiple in character whereas that of II was stepwise. These differences were rationalized in terms of the relative rates of desorption of II and III from the surface and the rate of formation of a tertiary carbonium ion from the initial olefin. The exchange reactions of the olefins with deuterium all occurred via a stepwise process.
CO2 poisoning of the γ-alumina-catalyzed reaction of COS with SO2
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (3), 1973) Chuang, T. T.; Lana, I. G. Dalla; Liu, C. L.
The poisoning of γ-alumina by CO2 has been shown to suppress the catalytic reaction, 2COS + SO2⇌(3/x)Sx+ 2CO2. Using infra-red spectroscopic evidence, a mechanism of reaction was postulated in which SO2 is adsorbed on hydroxyl sites and COS is adsorbed on aluminum ion sites. The latter sites become blocked through irreversible chemisorption of CO2. The postulated mechanism appears to explain other experimental observations.