Structure and behaviour of Ru3(CO)12 supported on inorganic oxide surfaces, studied by EXAFS, infrared spectroscopy and temperature-programmed decomposition

Abstract

The structure and behaviour of Ru3(CO)12 supported on inorganic oxides such as V2O5, SiO2, TiO2, Al2O3, K-Al2O3, MgO and MnO2 have been studied by means of EXAFS, IR and TPD. Ru3(CO)12 was physisorbed on V2O5, SiO2, and TiO2, whereas [Ru3(CO)10(µ-H)(µ-O)] and [HRu3(CO)11]– were formed on Al2O3 and the basic supports MgO and K-doped Al2O3, respectively, by the reaction of Ru3(CO)12 with the surface OH groups. Although [HRu3(CO)11]– was observed with MnO2, most of Ru3(CO)12 was oxidized on this surface. By the thermal decomposition of the supported clusters on V2O5 and SiO2, Ru metal and coordinatively unsaturated Ru3(CO)6 were formed, respectively, where no Ru—O bonding was observed by EXAFS. In contrast to these surfaces, on TiO2[Ru3(CO)6] was bonded to the surface oxygens to form [Ru3(CO)6(µ-OTi)3] with a Ru—O distance of 0.219 nm and an Ru–Ru distance of 0.275 nm. Similar structures, with different bond distances, were suggested for Ru3 clusters on K-Al2O3 and MgO. The monomeric Ru twin carbonyls [Ru(CO)2(OAl)2] which have the direct Ru—O bond of 0.218 nm in a bidentate form were formed on Al2O3. On the MnO2 surface, Ru oxide having Ru—O bonds of 0.200 nm was formed. The monomeric [Ru(CO)2(OAl)2] exhibited CO stretching at 2080 and 2030 cm–1. [Ru3(CO)6(µ-OTi)3] with a Ru–Ru distance of 0.275 nm showed peaks at 2081 and 2009 cm–1, while [Ru3(CO)6(µ-OZ)3](Z = Mg or Al) with the Ru–Ru distance of 0.271 nm showed peaks at 2040–2050 cm–1 and 1959–1975 cm–1. Peaks at 2067 and 2010 cm–1 were observed with [Ruo3(CO)6] on SiO2 with no direct chemical bonding to SiO2 surfaces. The different structures of the Ru twin carbonyl species produced on the various oxide surfaces are discussed in terms of the acidity or basicity of metal oxides and the strength of the support metal–oxygen bond.