Characterisation and Reactivity of Activated Carbon Supported Platinum Catalysts Prepared by Fluidised Bed Organometallic Chemical Vapour Deposition (FBOMCVD)

摘要

In the course of developing new methods for the preparation of heterogeneous catalysts, we have recently shown that the combinationof organometallic chemical vapor deposition (OMCVD) and the fluidization of a bed of porous particles is a powerful method to prepare supported catalysts (1). Highly dispersed deposits of rhodium, palladium and platinum on metal oxide supports were obtained in a single step using a fluidized bed reactor (2). The method of chemical vapor deposition (CVD) allows direct deposition of the active phase onto the catalyst support by means of the reation betwden surface sites contiaining oxygenated groups and the vapor of a suitable organometallic compound. Using silica or alumina with large specific areas-around 200 m~2g~-1.-the presence of hydroxyl groups on the surface allows the facile grafting of small and dispersed particles of the noble metal (2-5nm). On such support, the high concentration of anchoring groups presumably permits the maintenance of a high nucleation rate which favors the growth of the particles. For carbon supports the situation is somewhat different, since les sactive sites are available and these have a larger diversity in their chemical nature. Through careful oxidation processes, it is possible to control the nature and concentration of the oxygenated functions on the surface. As carbon supported catalysts play an important role in many catalytic reactions, we have undertaken a study in which we have examiend the suitability of the FBOMCVD method for the direct elaboration of such catalysts. The present report concerns the deposition of platinum on various carbon types. After preliminary OMCVD experiments on planar model supports, various activated carbon powders were examined for the elaboration of platinum supported catalysts. The activity of these catalysts was comapred with that of conventional wet impregnated catalysts in benzene hydrogenation.