A vibrational spectroscopic study of the thermal behavior of Re2(CO)10 on zeolite Y

Abstract

This work describes the thermal decomposition of Re2(CO)10 in zeolite Y, which generates the zeolite-supported complex Re0(CO)3(O-Z)3, where (O-Z) represents a framework oxygen. The adsorption and thermal decomposition of Re2(CO)10 was performed on dehydrated and hydrated zeolite NaY. The conversion to Re0(CO)3(O-Z)3 was not significantly affected by the presence of water within the supercages as the supported complex formed at around 200 °C no matter what the initial water content of the zeolite was. However, when the zeolite sample was treated at ≥200 °C for long periods, the adsorbed H2O became involved in the reactivity, playing a role as an oxidant. The subcarbonyl complex Re0(CO)3(O-Z)3 was oxidized, generating isolated Re2O7 or HReO4, or a mixture of both, which was dispersed inside the zeolite host. This result suggests that thermal decomposition of Re2(CO)10 on a hydrated zeolite under mild conditions can be a convenient route for preparation of zeolite-supported Re2O7 catalysts. Re0(CO)3(O-Z)3 was also formed in siliceous zeolite Y (SiY) upon heating. But it quickly decomposes into metal Re at around 200 °C, suggesting that the tricarbonyl species is destabilized in the almost natural zeolite framework. The present study also shows that FT-Raman spectroscopy is a useful technique for monitoring the behavior of the metal carbonyl species in zeolitic hosts.Key words: Raman spectroscopy, zeolite Y, rhenium carbonyl, rhenium oxide.