Density-functional calculations were performed to study hydrogen adsorption on Pt clusters and Pt surfaces. The calculations show that hydrogen atom adsorption energy on the clusters gradually decreases with increasing Pt cluster size. The adsorption on the facets of Pt-147 clusters is similar to that on the corresponding Pt surfaces. On the other hand, Pt-13, Pt-38, and Pt-55 clusters show quite different hydrogen adsorption behavior. (c) 2006 Elsevier B.V. All rights reserved.