Preparation and characterization of ultrathin [Ru(CO)3Cl2]2 and [BMIM][Tf2N] films on Al2O3/NiAl(110) under UHV conditions

Abstract

Towards a better understanding of the interface chemistry of ionic liquid (IL) thin film catalytic systems we have applied a rigorous surface science model approach. For the first time, a model homogeneous catalyst has been prepared under ultrahigh vacuum conditions. The catalyst, di-μ-chlorobis(chlorotricarbonylruthenium) [Ru(CO)₃Cl₂]₂, and the solvent, the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf₂N], have been deposited by physical vapor deposition onto an alumina model support [Al₂O₃/NiAl(110)]. First, the interaction between thin films of [Ru(CO)₃Cl₂]₂ and the support is investigated. Then, the ruthenium complex is co-deposited with the IL and the influence of the solvent on the catalyst is discussed. D₂O, which is a model reactant, is further added. Growth, surface interactions, and mutual interactions in the thin films are studied with IRAS in combination with density functional (DFT) calculations. At 105 K, molecular adsorption of [Ru(CO)₃Cl₂]₂ is observed on Al₂O₃/NiAl(110). The IRAS spectra of the binary [Ru(CO)₃Cl₂]₂ + [BMIM][Tf₂N] and ternary [Ru(CO)₃Cl₂]₂ + [BMIM][Tf₂N] + D₂O show every characteristic band of the individual components. Above 223 K, partial decomposition of the ruthenium complex leads to species of molecular nature attributed to Ru(CO) and Ru(CO)₂ surface species. Formation of metallic ruthenium clusters occurs above 300 K and the model catalyst decomposes further at higher temperatures. Neither the presence of the IL nor of D₂O prevents this partial decomposition of [Ru(CO)₃Cl₂]₂ on alumina.