Creation of substrate-accessible interfacial defect sites will bring about new catalytic discoveries because substrate binding and activation on these sites are pivotal for controlling reaction intermediate and product selectivity. The partial oxidation of pristine Cu2O can lead to an excellent selective oxidation catalyst (CuO/Cu2O). The CuO/Cu2O, containing embedded CuO nanodomains on the surface and possessing abundant coordinatively unsaturated copper sites at the CuO-Cu2O interface, shows very high activity toward C-C bond cleavage and excellent selectivity toward formamides in trialkylamines oxidation. This result is exceptional because the previous works mainly offer dealkylated amines via C-N bond cleavage. The unusual catalysis by CuO/Cu2O is attributed to the co-activation of oxygen and amines in close proximity at the CuO-Cu2O interface. The present study contributes a new concept of delicate controlling substrate-accessible interfacial active sites on pristine oxide surfaces, and also offers a novel formamide synthesis method by trialkylamine oxidation. (C) 2015 Elsevier Inc. All rights reserved.