Collision-Induced Dissociation and Infrared Photodissociation Studies of Methane Adsorption on V5O12+ and V5O13+ Clusters

Abstract

V5O12CH4(+) and V5O13CH4(+) clusters are generated from interactions of pregenerated V5O12(+) and V5O13(+) with CH4 in a fast flow reactor, respectively. The two adsorption complexes are then characterized by collision-induced dissociation (CID) and infrared photodissociation (IRPD) methods. The CID studies indicate that CH4 is molecularly adsorbed on V5O12(+) and V5O13(+). Each of the IRPD spectra of V5O12CH4(+) and V5O13CH4(+) has a broad red band located around 2770 cm(-1) and a narrow blue band located around 2990 cm(-1). The red and blue bands have large and small red shifts with respect to the symmetric and antisymmetric C-H stretch vibrations of free CH4, respectively. Density functional theory calculations are carried out for the structures and vibrational frequencies of V5O12(+) and V5O12CH4(+). The computed results suggest that the anharmonicity including Fermi resonance should be taken into account to interpret the observed IRPD spectrum. In V5O12CH4(+), the CH4 unit adsorbs on the 3-fold coordinated V(5+) site with an η(2) configuration. The stretch of the two C-H bonds close to the V(5+) ion is associated with the red band and the stretch of the other two C-H bonds is associated with the blue band. This study may shed light on the nature of methane adsorption onto vanadium pentoxide surfaces.