Abstract
Reduction of bismuth phosphate (Bi/P=2) and of stannic oxide containing small amounts of Na20 with propylene were studied at 500-800°C, in connection with their catalytic properties in the oxidative dehydroaromatization of lower olefins.
X-ray diffraction analyses (Figs.2 and 6) showed that bismuth phosphate catalyst, which was composed of 3 Bi203.P205, 2 Bi203. P205, monazite form 0-BiPO4, high temperature form T-BiPO, and T-Bi203, and stannic oxide catalyst were reduced as follows:
Main products from propylene during reduction were carbon dioxide and benzene in both cases, where the initial compositions were the same as those in the catalytic oxidation. These facts indicate that the oxidative dehydroaromatization proceeds by the redox mechanism of the catalyst (Bi3+ ⇔ Bi or Sn4+ ⇔ Sn). With the progress of reduction, the amount of CO2 formed decreased monotonously in every case. However, that of benzene formed showed different behaviors from CO2 as shown in Figs.1, 4 and 5. The selectivity of benzene formation decreased with the reaction time at lower temperatures where the reduction rate was relatively small, while the selectivity increased at higher temperatures. These complicated behaviors are presumably related to the concentration and the mobility of oxygen ion and/or allylic intermediate on the catalyst surface.
