Reaction of N-2 with H2O on gas-phase tungsten clusters W-n(+) (n = 3-5), probably yielding N2O, was observed at room temperature. Distinct cluster size dependence of N-2 activation was found: N-2 is activated by W-4(+) and W-5(+) to a much greater extent than by W-3(+). The N-2 activation is made possible by bridge adsorption geometry on the clusters. A notable observation is that such an activated N-2 adsorption state, that exists only at low temperatures on bulk metal surfaces, survives at room temperature on the tungsten clusters. This is due to the high dissociation barrier for N-2 on the clusters. (C) 2016 Elsevier B.V. All rights reserved.