The characterisation of a model platinum/alumina catalyst by high-resolution electron microscopy

Model catalysts consisting of platinum particles on a thin alumina support were examined by electron microscopy following various oxidative and reducing treatments. Details of particle size distributions were obtained and particle sintering was shown to depend on treatment temperature, atmosphere, and metal loading, being greatest in a "chlorided" oxygen environment and least in a pure hydrogen one. Trace impurities, even at the 1-vpm level, were shown to enhance significantly the sintering rate in a reducing atmosphere. High-resolution observations at the direct lattice imaging level provided information about both particle and support morphology, in particular establishing that most particles consist substantially of metallic platinum, either in single-crystal form or often twinned. The relevance of model catalyst studies to "real" catalysts is briefly discussed.