PARTICLE-SIZE EFFECTS IN ELECTROCATALYSIS BY UNIFORM COLLOIDS OF RUTHENIUM DIOXIDE HYDRATE

A series of monodisperse, sterically stabilized colloids of electrocat alytically active ruthenium dioxide hydrate (RuO2.XH(2)O) with diamete rs between 40 and 160 nm are used to examine the relationship between particle size, catalyst concentration, and the heterogeneously catalyz ed rate of water oxidation by cerium(IV) ions in dilute nitric acid. R eaction rate is linearly dependent upon catalyst concentration for all particle sizes. Rate constants vary with particle radius raised to th e power -1.7 and exhibit absolute values consistent with mass transfer of Ce-IV ions to the catalyst surface being the rate-limiting step. A ctivation energies are found to decrease with particle radius, and thi s effect is attributed to the influence of the steric stabilizer upon the temperature-dependent viscosity of solution near the catalyst surf ace.