ToF-SIMS studies of the regeneration of Pd/TiO2 catalyst used in hydrodechlorination process

This paper is devoted to the surface studies of deactivation-regeneration process of Pd/TiO2 catalyst used in the hydrodechlorination of CCI4. The samples were prepared by the incipient wetness impregnation method. The time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used as a main analytical tool in these investigations. The advantages of this technique result from high sensitivity of secondary ion mass spectrometers, possibility of detection of not only elemental but also molecular ions and the fact that ToF-SIMS can give information from the upper layer of the investigated material. The results of ToF-SIMS measurements of as prepared, deactivated and regenerated specimens showed that the regeneration of the deactivated sample in the O-2 atmosphere among other causes an increase in the ability of the catalyst to the formation of palladium chloride in the next working cycles. A growth in the amount of PdCl2 was accompanied by a decrease in the quantity of surface accessible palladium atoms. It resulted in a more violent drop in the conversion of CCI4 and faster deactivation of the regenerated catalyst. The observations described above indicate that not only carbon deposition and deterioration of the surface area of the catalyst are serious problems in the hydrodechlorination process. The bigger attention should also be focused on the prevention of the formation of palladium chloride in the next working cycles of the catalyst after its regeneration. (C) 2010 Elsevier B.V. All rights reserved.