Control of surface structure at the atomic level can effectively tune catalytic properties of nanomaterials. Tuning surface strain is an effective strategy for enhancing catalytic activity; however, the correlation studies between the surface strain with catalytic performance are scant because such mechanistic studies require the precise control of surface strain on catalysts. In this work, a simple strategy of precisely tuning compressive surface strain of atomic-layer Cu2O on Cu@Ag (AL-Cu2O/Cu@Ag) nanoparticles (NPs) is demonstrated. The AL-Cu2O is synthesized by structure evolution of Cu@Ag core-shell nanoparticles, and the precise thickness-control of AL-Cu2O is achieved by tuning the molar ratio of Cu/Ag of the starting material. Aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) and EELS elemental mapping characterization showed that the compressive surface strain of AL-Cu2O along the  and  directions can be precisely tuned from 6.5% to 1.6% and 6.6% to 4.7%, respectively, by changing the number of AL-Cu2O layer from 3 to 6. The as-prepared AL-Cu2O/Cu@Ag NPs exhibited excellent catalytic property in the synthesis of azobenzene from aniline, in which the strained 4-layers Cu2O (4.5% along the  direction, 6.1% along the  direction) exhibits the best catalytic performance. This work may be beneficial for the design and surface engineering of catalysts toward specific applications.[Figure not available: see fulltext.].
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