||The surface of transition metals are critical to their catalytic properties. These surfaces can be mimicked by clusters, which are aggregates of atoms. The Smalley-type cluster ion source provides a simple way to produce metal clusters with two, three, up to hundreds of atoms. Niobium is selected for this research not only because the bond between niobium atoms is relatively large (550 KJ/mol), but also because it is isotopically pure. The reactions between niobium clusters with simple molecules have attracted broad interest over the last 15 years. The reactions with H2, D2, N2, O2, CO2, CO, C6H6 were found to show strong dependence on the cluster size.