抄録
The roles of Fe, Li and As components of the Fe-Li-As oxide catalyst in the vapour phase oxidation of propylene have been investigated in connection with the activity and structure of the catalyst. The reaction kinetics has also been studied. The experiment of the catalytic reaction was carried out in the temperature range of 400∼470°C, with 12∼25% propylene in air. Pulse method was used to clarify the behaviour of the surface oxygen, the activity of reduced catalyst and the roles of catalyst components. X-ray measurements were also made in order to study the structure of catalyst.
The rates of formation of acrolein and carbon dioxide are first order in propylene and independent of oxygen. Two structures of -Fe-O-As- and -Li-O-As- are observed in the catalyst; the former is thought to be more easily reduced by propylene than the latter. It is considered that the catalytic oxidation is mainly carried out at two different active sites, both being contained in the -Fe-O-As- structure, through a redox-cycle consisting of
As5+C3H6→As3+and As3+O2→(fast)As5+.
The formation of acrolein occurs at one site and that of carbon dioxide at the other site. The -Li-O-As- structure is considered to be instrumental in preventing the escape of As component into vapour phase. A slightly reduced catalyst shows higher activity of synthesizing acrolein by reaction with propylene.
