HYDROCARBON REACTIONS ON AN OXIDIZED PLATINUM SILICON ALLOY MODEL CATALYST

An oxidized platinum silicon alloy model catalyst obtained by oxidation of a Pt97Si3 bulk alloy was tested in the reactions of hexanes. Such a model catalyst was designed to simulate supported catalysts such that it can be submitted to surface investigations and also catalytic reactions in conditions similar to those used in single-crystal studies, without any exposure to air. The catalytic behaviour of the alloy (Pt97S3)Ox surface is interpreted according to a model of platinum crystallites dispersed on or in SiO2 and probably presenting steps, edges and comers constituted of Pt atoms instead of large (111) or (100) terraces. Such a model surface has very different properties from those of very small clusters of Pt deposited on Al2O3 or SiO2 and shows the important role of defects for the reactions of labelled hexanes not only for the overall activity and selectivity but also for the resistance to coke formation which must be initiated on large terraces of Pt atoms.