Various acido-basic BEA zeolites having different Cs contents and containing supported Pt particles were prepared using two acidic parent BEA supports with same framework A1 content but with strongly different morphology of the zeolite crystallites. In spite of highly different exchange capacities in aqueous solution, the two parent BEA supports behaved similarly towards formation of Cs-oxide like nanospecies. Thus, the addition of a similar amount of Cs was necessary in the two samples to extinguish all Bronsted acidic sites and a further introduction of Cs led to the presence of highly dispersed Cs2O like species with strong basic character as shown by the adsorption of CO2 followed at 293 K by FT-IR spectroscopy. FT-IR experiments were also conducted at 100 K and 293 K using CO as probe molecule to give further insights on the Cs and reduced Pt species, respectively. In the presence of co-hosted Cs-oxide like, highly dispersed Pt-0 nanoparticles are formed with sizes close to 1 nm as observed by TEM. Both the high dispersion of the Pt-0 nanoparticles in the more basic samples and the phenomenon of electro-donation by the basic support contribute to the changes in electronic behaviour of the Pt particles shown by FT-IR of adsorbed CO. (c) 2007 Elsevier B.V. All rights reserved.