Chemistry of supported Ru: CO-induced oxidation of Ru at 310 K

Abstract

Infrared spectra of CO on reduced titania-supported Ru show three bands at 2060, 2085, and 2140 cm −1. The first band saturates almost instantly in excess CO and exhibits coverage-dependent frequencies at subsaturation which are consistent with its assignment to CO in on-top sites on the anticipated Ru crystallites. The latter two bands grow slowly as a pair in several Torr CO at 310 K, and their growth rate is accelerated at 400 K. IR spectra measured in mixtures of isotopically labeled CO show the two high-frequency bands represent coupled vibrations of an Ru(CO) x ( x > 2) species. The observed frequencies correlate with those expected for a Ru(II) species and XPS shows that a fraction of the zero-valent Ru present on a reduced sample is converted to a higher valent species upon exposure to CO at 310 K. We therefore assign the 2085- and 2140-cm −1 IR bands to (TiO) 2Ru(CO) 3 surface species. We also propose these species form via an oxidative fragmentation reaction involving zero-valent Ru, CO, and surface hydroxyls on the support.