The activity-selectivity patterns of Pd/pumice catalysts are compared with industrial and home prepared Pd/Al2O3 catalysts in the hydrogenation of acetylene in ethylene rich feedstocks (front-end and tail-end cuts). The iso-kinetic relationship (IKR) approach and a new mathematical model, surface site evolution model (SSEM), are employed in this comparison. Pumice and alumina supported Pd catalysts show different metal redox properties. A similar reaction mechanism is adequate to describe the reaction pathway independently by the catalysts and the gas mixtures considered. This mechanism involves the formation of surface polymers during the catalytic reactions and different catalytic sites which are discriminated on the basis of the different steric interactions of the reagents with the surface species. Although the surface mechanism appears to be analogous for all the Pd catalysts considered, industrial Pd/Al2O3 and Pd/pumice catalysts show a different activity-selectivity pattern as a consequence of their different electron density and ensemble size.