Abstract
There has been considerable interest in recent years in the effects of doping of light metal materials with transition metals to improve the thermodynamics and kinetics of hydrogen chemisorption and desorption. Foremost among these is the work of Bogdanovic and Schwickardi (1997) who demonstrated that doping alkali metal hydrides with a few mol% of Ti can lead to reversible decomposition at reasonable temperatures and pressures. Theoretical studies (Chaudhuri 2005, 2006) of Ti-doped NaAlH 4 indicate that the Ti dopant is responsible for catalysing H 2 chemisorption when the Ti atoms are in specific local arrangements. The reactivity, electrostatic fields and surface features of small metal clusters can differ significantly from that of bulk materials and is often dependant on not only the composition but the size of the cluster. While theoretical and experimental studies have shown that the interaction of hydrogen atom with aluminium clusters is thermodynamically favoured, experimental studies have suggested that the kinetics for chemisorption of hydrogen molecule on pure aluminium clusters are quite slow. Experimental studies of the interaction of molecular hydrogen with aluminium clusters have generally been carried out in the gas phase with charged clusters to enable isolation and detection of the products (Cox, 1988) (Jarrold, 1988). In this study we investigate the interaction of diatomic hydrogen with a series of neutral and charged X-centred aluminium clusters (Al 12X, X = Mg, Al, Si). We use the PBE/6-311G(d, p) and PBE/DNP levels, which have been found to give close agreement with CCSD/6-31G(d, p) for the ground state structures of Al 12X clusters and ions (Henry, 2008).