The thermal evolution of mania-supported Au shell-Pd core bimetallic nanoparticles prepared via colloidal routes has been investigated by in situ XPS DRIFTS EXAFS and XRD and ex situ HRTEM As-prepared nanoparticles are terminated by a thin (similar to 5 layer) Au shell encapsulating approximately 20 nm diameter cuboctahedral palladium cores with the ensemble stabilised by citrate ligands The net gold composition was 40 atom% Annealing in vacuo or under inert atmosphere rapidly pyrolyses the citrate ligands but induces only limited Au/Pd intermixing and particle growth <300 C Higher temperatures promote more dramatic alloying accompanied by significant sintering and surface roughening These changes are mirrored by the nanoparticle catalysed liquid phase selective aerobic oxidation of crotyl alcohol to crotonaldehyde palladium surface segregation enhances both activity and selectivity with the most active surface alloy attainable containing similar to 40 atom% Au (C) 2010 Elsevier B V All rights reserved