SURFACE-STRUCTURE CHANGE OF A [PT-4(MU-CH3COO)(8)] SIO2 CATALYST ACTIVE FOR THE DECOMPOSITION OF FORMIC-ACID/

Pt-4-cluster/SiO2 catalyst, prepared from the [Pt-4(mu-CH3COO)(8)] clu ster, has shown remarkably high catalytic activity with 100% selectivi ty to CO2 and H-2 for the decomposition of formic acid as compared wit h the Pt-particle/SiO2 catalyst. In order to elucidate the genesis and the mechanism for catalysis by Pt-4-cluster/SiO2, the samples were ch aracterized by kinetics, Pt L(III)-edge extended X-ray absorption fine structure (EXAFS), and FTIR spectroscopy. EXAFS and IR data revealed that the surface structure of the catalyst changed from the tetramer t o dimers during an induction period, then to monomers which were activ e for the catalysis. Eventually Pt particles were formed which were of much lower catalytic activity. The structural transformations of the Pt-4-cluster/SiO2 catalyst are discussed in relation to the catalytic reaction profiles.