Effect of Lanthana as a Stabilizing Agent in Titanium Dioxide Support

The thermal stability of between 1 and 5 wt % lanthana-doped TiO2 was investigated. Three methods of aging the titania support were studied: stagnant air heating for 12 h at temperatures ranging from 450 to 900 °C, flowing humid 450 °C air for up to 25 days, and flowing humid 650 °C air for up to 30 days. The thermal stability was assessed using BET surface area and XRD. Chlorodifluoromethane (HCFC22) oxidation was used as a probe reaction to determine the effects of thermal aging on the reactivity of the catalyst. The XRD results indicate that the decrease in surface area corresponds to the phase transformation from anatase to rutile. In the fixed time results, all doping levels achieved the same elevated stability, increasing the phase transition temperature from approximately 450 to about 650 °C. However, when the support was aged by exposure for an extended time, increasing the lanthana loading increased the thermal stability. This surface area thermal stability was shown to be related to the activity of the catalyst in oxidizing HCFC22.