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 (C₁, C₂, C₃, C₄). As the wet oxidation proceeded, the C₁ peak increased gradually with reaction time, whereas the C₂ and C₃ peaks passed through maxima. At around the C₂ and C₃ peak maxima, the C₄ peak began to appear and increased continuously up to 10 h reaction. This result indicates that at least two carbonaceous materials of C₂ and C₃ 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.