Modeling of Catalyst Sintering and Study of Accelerated Aging Based on Pt/Al2o3 as a Model Catalyst

Precious metal catalysts, such as Pt/Al₂O₃, are the primary active ingredient in diesel oxidation catalysts (DOC) used to control CO, HC and SOF emissions. Sintering of precious metal is one of the main deterioration factors of catalytic performance. In hot applications sintering of the alumina support material has also been suggested to accelerate precious metal sintering. Investigation of sintering rates may allow estimation of the catalyst life and provide information important for catalyst durability improvement. In this study, Pt/Al₂O₃ was used as a model catalyst and a sintering model for thermal aging was constructed. Pt sintering could be expressed by a differential equation which includes both Pt and support material sintering, but better fit to experimental data resulted from inclusion of a factor that includes an Al₂O₃ phase change. A prediction of catalytic performance after aging was attempted using this Pt/Al₂O₃ sintering model but the catalytic performance deterioration could not be simply expressed by only the Pt sintering.

Accelerated aging was also studied by changing the aging temperature and time period to understand the relationship between catalytic performance and the physical properties of catalyst, i.e. surface area of the Pt particle, specific support surface area and crystal phase of the support material. Such accelerated aging is sometimes performed for engineering purposes, catalyst development and quality control of the catalyst product. For this Pt/Al₂O₃ model catalyst, 800 degreesC/200hr aging was almost equivalent to 900 degreesC/50hr and 1000 degreesC/10hr agings in both catalytic performance (HC T50, CO T50) and physical characteristics (phase change of Al₂O₃), although surface area of the Pt particles varies slightly.