Various surface probe techniques were applied to investigate the decomposition of methanol on partially alumina-encapsulated Pt nanoclusters on an ordered thin film of Al2O3/NiAl(1 0 0). The alumina-encapsulated Pt clusters were prepared on annealing Pt clusters (grown by vapor deposition onto the Al2O3/NiAl(1 0 0) at 300 K) to 650 K under UHV conditions. The annealed cluster became a Pt1+-Pt2+ state and partially encapsulated with inert alumina. Methanol on the partially encapsulated Pt clusters decomposed only on the uncovered Pt sites, and through both dehydrogenation to CO and scission of the C-O bond. In comparison to the reactions on Pt clusters, the C-O bond scission was altered little on the partially encapsulated clusters whereas the dehydrogenation was hindered to a certain extent. The quantities of CO and hydrogen produced from the dehydrogenation per surface Pt on the partially encapsulated clusters amounted to only half those on Pt clusters. The altered methanol decomposition was correlated to both electronic and ensemble effects. (C) 2014 Elsevier B.V. All rights reserved.