CARBON DEPOSITION ON SUPPORTED PLATINUM PARTICLES

A combination of electron microscopy and thermogravimetric techniques have been used to investigate the characteristics of coke formation and the associated changes in platinum particle morphology in real and model reforming catalysts. Despite the fact that used commercial catalysts contained large amounts of coke, metal particles were clearly evident and appeared to reach an average size of 1.7 nm, indicative of only a limited degree of sintering during the reforming reaction. Decoking studies showed that the deposit was predominantly isotropic in nature and did not contain any filamentous or graphitic components. In situ electron microscopy studies performed on model supported platinum catalyst systems showed that upon reaction in a hydrocarbon environment, the metal particles were capable of hydrogasifying carbon in their immediate vicinity and during this process underwent a wetting and spreading action at the deposit interface which resulted in redispersion of the platinum. This phenomenon was limited to a narrow temperature range between 480 and 600°C, and was believed to be a key factor in the maintenance of the small metal particle size during the reforming reaction. © 1990.