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-Al 2 O 3 , TiO 2 , CeO 2 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 Al 2 O 3 , TiO 2 and CeO 2 , even at high GHSV. CO, CH 3 Cl and CH 2 O were the major by-products observed and their amounts decreased after Pt impregnation. The CH 3 Cl formation was higher when Lewis acid sites were present while the existence of Brønsted sites promoted the CH 2 O formation. The complete conversion of DCM was achieved at around 450 °C over the Al 2 O 3 and Pt/Al 2 O 3 and at 500°C for Pt/TiO 2 . These two catalysts exhibited the highest total acidities among the materials tested. The activity of Pt/Al 2 O 3 remained the same also after 55 h of testing, however, increase in Pt particle size and decrease in acidity were observed. Pt/CeO 2 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.
In the present research, an industrially aged Pt/Al2O3 catalyst was used as a basis for the study on the sulfur deactivation and the development of more resistant catalytic materials. The catalytic activities of both industrially and laboratory-aged materials in DMDS oxidation were studied in addition to characterization by XRD, XPS, FESEM, TEM and N2 adsorption. The industrial ageing induced a phase change from γ-Al2O3 towards θ-Al2O3, formation of aluminum sulfates and an increase in Pt particle size as well as a change in the oxidation state of Pt to a higher state. These changes caused an increase of 30°C in the light-off temperature for DMDS oxidation. Accelerated ageing in the presence of SO2 and H2O vapor at 400°C for 5 h decreased the activity of the Pt/Al2O3 at the same level than for the industrially aged catalyst even though smaller sulfur content and no sintering of γ-Al2O3 were observed. Pt sintering (10-20 nm) in both cases was observed. The XPS results confirmed the formation of new sulfate phases and the interaction between sulfur and the active phase as well as the support of the catalyst undergone accelerated ageing. After the accelerated ageing of copper-based catalysts, the 0.3Pt10Cu/Al2O3|0.8SiO2|0.2 catalyst showed an interesting resistance towards sulfur deactivation, as it was expected.
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