Abstract

The aim of this work was to study the influence of the support oxide properties on the total oxidation of dichloromethane in moist conditions. The support materials γ-Al₂O₃, TiO₂, CeO₂ and MgO were synthesized by a sol-gel method followed by wet impregnation of Pt and characterized by different physico-chemical techniques. The conversion of DCM was higher than 90% at 500 °C over impregnated and non-impregnated Al₂O₃, TiO₂ and CeO₂, even at high GHSV. CO, CH₃Cl and CH₂O were the major by-products observed and their amounts decreased after Pt impregnation. The CH₃Cl formation was higher when Lewis acid sites were present while the existence of Brønsted sites promoted the CH₂O formation. The complete conversion of DCM was achieved at around 450 °C over the Al₂O₃ and Pt/Al₂O₃ and at 500 °C for Pt/TiO₂. These two catalysts exhibited the highest total acidities among the materials tested. The activity of Pt/Al₂O₃ remained the same also after 55 h of testing, however, increase in Pt particle size and decrease in acidity were observed. Pt/CeO₂ while being less active showed smallest amount of by-product formation during the whole temperature range used in light-off tests. This is most probably due to its easy reduction ability. The textural parameters of the supports did not appear to be the key parameters when considering the activity and selectivity of the catalysts.