There has been debate in the past as to whether or not cyclopropane hydrogenolysis is a structure sensitive reaction. This paper addresses the structure sensitivity of cyclopropane hydrogenolysis on Pt using K(+) addition to Pt/C and compares the results to those for CO hydrogenation, a classic structure insensitive reaction. Kinetic parameters determined for both reactions show the effect of K(+) on Pt to be limited to simple site blockage at the reaction conditions used. Determination of the site ensemble size (number of contiguous surface metal atoms) required for reaction using Martin's model suggests that cyclopropane hydrogenolysis requires a site ensemble size of ca. 7, whereas the structure insensitive CO hydrogenation reaction requires only an ensemble size of ca. 1. In addition, evidence suggests that K(+) decorates Pt non-uniformly. (C) 2011 Elsevier Inc. All rights reserved.