LETTERS nature materials | ADVANCE ONLINE PUBLICATION | www.nature.com/naturematerials 1 Controlling the catalytic bond-breaking selectivity of Ni surfaces by step blocking

The reactivity of catalytic surfaces is oft en dominated by very reactive low-coordinated atoms such as step-edge sites1–11. However, very little knowledge exists concerning the infl uence of step edges on the selectivity in reactions involving multiple reaction pathways. Such detailed information could be very valuable in rational design of new catalysts with improved selectivity. Here we show, from an interplay between scanning tunnelling microscopy experiments and density functional theory calculations, that the activation of ethylene on Ni(111) follows the trend of higher reactivity for decomposition at step edges as compared with the higher-coordinated terrace sites. Th e step-edge eff ect is considerably more pronounced for the C–C bond breaking than for the C–H bond breaking, and thus steps play an important role in the bond-breaking selectivity. Furthermore, we demonstrate how the number of reactive step sites can be controlled by blocking the steps with Ag. Th is approach to nanoscale design of catalysts is exploited in the synthesis of a new high-surface-area AgNi allo