Particle-size dependent heats of adsorption of CO on supported Pd nanoparticles as measured with a single-crystal microcalorimeter

We present calorimetric measurements of the effect of cluster size on the adsorption enthalpy of carbon monoxide on Pd nanoclusters sized from 120 to 4900 Pd atoms per particle, which were grown in situ on a well-ordered Fe ₃O₄/Pt (111) film. A substantial decrease in the initial heat of adsorption amounting to about 20-40kJ mol^-1 was observed on the smallest Pd nanoparticles as compared to the larger Pd clusters and the extended Pd(111) single-crystal surface. We discuss this effect in terms of the size-dependent properties of the Pd nanoparticles.