THE INFLUENCE OF PARTICLE-SIZE ON CO OXIDATION ON PD ALUMINA MODEL CATALYST

The CO oxidation on Pd(111) and small Pd particles deposited on an alumina support has been studied by means of the thermal molecular beam technique using the transient method at temperatures between 300 and 500 K. The surface is predosed with a known coverage of oxygen and then exposed to the beam of carbon monoxide at a given temperature until the reaction is complete, The temperature anti coverage dependent CO oxidation data were obtained for alumina supported Pd particles as well as for a Pd(111) single crystal. The activation energy of the Langmuir-Hinshelwood reaction was calculated for all samples. It was found that the small particles were more reactive. The activation energy E of CO oxidation on 2.5 nm particles is 19 kJ/mol whilst it is 45 kJ/mol for a Pd(111) single crystal. The long-time CO2 production during the transient CO oxidation on small Pd particles, compared to the Pd(111), is explained by the diffusion of oxygen atoms into the subsurface region of Pd particles.