A series of Rh nanoparticles with sizes between 3.5 and 11.4 nm were synthesized in the presence of polyvinylpyrrolidone and evaluated for their performance as catalysts in the hydrogenation of phenylacetylene and 1-octene. The reaction is zeroth order in the reactant for phenylacetylene and 1-octene. The catalytic activity increased with Rh particle size in the hydrogenation of phenylacetylene, whereas the activity in 1-octene hydrogenation did not depend on particle size. The possible explanations for this different particle size behavior are discussed. (C) 2011 Elsevier B. V. All rights reserved.