Encapsulation of Tetracarbonyl(trimethylstanny1)cobalt in NaY Zeolite: Reactivity and Alloy Cluster Formation

A bimetallic precursor route toward the encapsulation of subnanometer tin-transition metal alloy clusters in zeolites is presented. The intrazeolite chemistry and thermal stability of MesSnCo(CO)4 in NaY zeolite were studied with X-ray absorption spectroscopy (Sn, Co edge EXAFS) and in-situ FTIR/TPD-MS techniques. In the NaY host, the intact precursor is physically adsorbed from hexane solution into the dehydrated zeolite cages at room temperature without further chemical reaction. Symmetry changes of the Co(C0)4 moiety indicate interaction of the CO ligands with the Na+ ions of the zeolite framework. The intrazeolite complex in NaY is accessible to external reactants and undergoes carbonyl substitution with PMe3 at the cobalt center. The encaged organometallic complex is stable up to about 90 “C and then decomposes by loss of CO ligands and rearrangement of the Sn-Co structure, resulting in metal clusters with bridging carbonyl ligands. At about 300 OC, all CO is removed, and very small tin-cobalt alloy clusters are formed as detected with EXAFS spectroscopy. This process is also observed in porosity measurements showing successive recovery of free volume on CO removal.