In this work, we address the stability of platinum nanoparticles (Pt-NPs) encapsulated in alumina. Colloidal Pt-NPs capped with poly(N-vinyl-2-pyrrolidone) (PVP) were prepared and enclosed in an oxide matrix by incorporating them during the sal-gel synthesis of boehmite. PVP/Pt molar ratios of 0.2 and 10 produced particles with similar average diameters (<3 nm) but showed very different thermal stability in the alumina support. We investigated the calcination process and the phase transition of the support (boehmite to gamma-Al2O3) by several techniques, showing that Pt-NPs catalyzed PVP decomposition at lower temperature than required for dehydroxylation of boehmite, causing sintering of the Pt-NPs when the PVP/Pt ratio was low. The results showed that a high PVP/Pt ratio was required to encapsulate and stabilize the Pt-NPs in the gamma-Al2O3 support, having a direct impact in the catalytic performance of the materials in the water gas shift reaction. (C) 2014 Elsevier B.V. All rights reserved.