Complete oxidation of o-xylene over Pd/Al 2O 3 catalyst at low temperature

Abstract

The catalytic activities of γ-Al 2O 3 supported noble metal (Pd, Pt, Au, Ag, Rh) catalysts were tested and compared for catalytic oxidation of o-xylene. The results show that Pd/Al 2O 3 is the most active catalyst among these noble metal catalysts. The effects of Pd loading and gas hourly space velocity (GHSV) on the activity of Pd/Al 2O 3 catalyst for o-xylene oxidation were investigated at low temperature from 60 to 190 °C. At 1 wt% Pd loading, 100 ppm o-xylene can be completely oxidized to CO 2 and H 2O at ca.110 °C over the Pd/Al 2O 3 catalyst at a GHSV of 10,000 h −1. The 1% Pd/Al 2O 3 was characterized using BET, XRD methods. The XRD patterns showed that PdO was the dominant species in the fresh Pd/Al 2O 3 catalyst and metallic Pd was the main phase in both the H 2 pretreated and the used catalysts. The metallic Pd is proposed to be the active species for o-xylene oxidation. The mechanism of o-xylene oxidation was studied with respect to the behavior of adsorbed species on Pd/Al 2O 3 surface examined by in situ DRIFTS and the gas products detected by the online GC/MS. On the basis of experimental results, a simplified mechanism for the catalytic oxidation of o-xylene over Pd/Al 2O 3 was proposed.