Comparative study on the support properties in the total oxidation of dichloromethane over Pt catalysts

- Total conversion of dichloromethane was reached at 450 °C over Al2O3 and PtAl2O3.
- Formation of by-products over PtTiO2 and PtCeO2 is smaller than over PtAl2O3.
- Dichloromethane oxidation is influenced by the nature and quantity of acid sites.
- By-products formation is influenced by acid sites and catalyst reducibility.
- Pt/Al2O3 showed good activity even after 55 h of stability test.

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.

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