In this work a kinetic analysis based on the two-step reaction and Langmuir-Hinshelwood mechanisms is applied to the aqueous phase hydrodechlorination of 4-chlorophenol catalyzed by unsupported Rh nanoparticles. The theoretical predictions of the models based on the two-step and Langmuir-Hinshelwood methods showed good agreement with experimental activity data (turn over frequency) from reaction runs carried out at 303 K with nanoparticles of different sizes (1.9-4.9 nm). The theoretical maximum activity (29-30 h(-1)) was predicted for nanoparticle sizes of 2.5-2.7 nm, very close to experimental values (ca. 28 h(-1), 2.8 nm). The applicability of the two-step reaction and Langmuir-Hinshelwood mechanism to unsupported metal nanoparticles is proved and mechanistic information is obtained. An important difference in the Gibbs replacement adsorption energy (100-130 kJ mol(-1)) of hydrogen by chlorophenol has been found between edges and terraces.