Catalytic Wet Oxidation of Phenol Using Regeneration of Pt/Al2O3

Abstract

Removal of phenol by wet air oxidation was conducted with 1 wt% Pt/Al2O3 catalyst in a batch reactor and in a continuous flow fluidized bed reactor with air lift tube operated at 423 K and 1.4 MPa. After 60 min in the batch reactor with initial phenol concentration of 1000 mg/l, almost complete conversion into CO2 and H2O was achieved. Pt/Al2O3 catalyst deactivation was observed during the wet oxidation reaction. TEM, EDX, XPS and TPO analyses showed the deactivation was caused by formation and deposition of carbonaceous materials on the catalyst surface. TEM of the deactivated Pt/Al2O3 showed formation of filamentous materials, which linked Pt particles, and some Pt particles were completely encapsulated by deposited material. XPS analysis showed that the carbonaceous materials on the catalyst consisted of four different morphologies (C-1, C-2, C-3, C-4). As the wet oxidation proceeded, the C-1 peak increased gradually with reaction time, whereas the C-2 and C-3 peaks passed through maxima. At around the C-2 and C-3 peak maxima, the C-4 peak began to appear and increased continuously up to 10 h reaction. This result indicates that at least two carbonaceous materials of C-2 and C-3 were transformed morphologically into C4 material. The broad profiles of CO2 formation from the TPO experiment implied that at least two types of carbon deposits were oxidized at different temperatures, one type on Pt particles, the other type on Al2O3. The carbonaceous deposit was formed on Pt particles and migrated continuously onto the support. The continuous flow fluidized bed reactor showed very stable wet oxidation performances in the presence of the air lift tube. The air lift tube was important in continuously regenerating the deactivated catalyst. The accumulated carbon deposits were reduced drastically by the action of the air lift tube.