The oxidatian by Co(NH3)(5)Cl2+ of N,N,N＇,N＇, tetramethyl-p-phenylenediamine (TMPPD) catalyzed by nanoparticles of palladium in an aqueous buffer/AOT/n-heptane microemulsion has been studied. The initial rates of reaction varied proportionately with the Co(NH3)(5)Cl2+ concentration, increased slightly with increasing TMPPD concentration, and rose linearly with the palladium concentration up to ca. 6 mu M. However, a much steeper increase was discovered at higher catalyst concentrations. Evidence that adsorption of TMPPD on the palladium surface was playing a major role in the rate-determining step was obtained both from the fact that the activation energy at 15 degrees C was more than twice as large as that at 40 degrees C and from electrochemical experiments with the two reactants. A microreactor model for catalyst particles in microemulsion water pools was set out, and the resulting water pool sizes and numbers have been evaluated.