Complete oxidation of o-xylene over Pd/Al2O3 catalyst at low temperature

The catalytic activities of gamma-Al2O3 supported noble metal (Pd, Pt, Au, Ag, Rh) catalysts were tested and compared for catalytic oxidation of o-xylene. The results show that Pd/Al2O3 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/Al2O3 catalyst for o-xylene oxidation were investigated at low temperature from 60 to 190 degrees C. At 1 wt% Pd loading, 100 ppm o-xylene can be completely oxidized to CO2 and H2O at ca.110 degrees C over the Pd/Al2O3 catalyst at a GHSV of 10,000 h(-1). The 1% Pd/Al2O3 was characterized using BET, XRD methods. The XRD patterns showed that PdO was the dominant species in the fresh Pd/Al2O3 catalyst and metallic I'd was the main phase in both the H-2 pretreated and the used catalysts. The metallic I'd 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/Al2O3 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/Al2O3 was proposed. (C) 2008 Elsevier B.V. All rights reserved.