Role of steps in N-2 activation on Ru(0001)

Using adsorption experiments and density functional calculations we show th at N-2 dissociation on the Ru(0001) surface is totally dominated by steps. The measured adsorption rate at the steps is at least 9 orders of magnitude higher than on the terraces at 500 K, and the corresponding calculated dif ference in activation energy is 1.5 eV. The low barrier at the step is show n to be due to a combination of electronic and geometrical effects. The con sequences for Ru as a catalyst for ammonia synthesis are discussed.