Low temperature dissociation of CO at reactive step sites of Pd(112)

CO adsorption at Pd(112) has been studied by means of Fourier-transform infrared reflection absorption spectroscopy and temperature programmed desorption (TPD) at 120 K. Pd(112) exhibits terraces of hexagonal closed packed palladium atoms ((111) orientation) with a width of three atoms and monoatomic steps of (100) orientation. In real catalysts consisting of nanocrystalline palladium particles on oxidic supports neighbouring facets of (111) and (100) orientation may be found. Pd(112) therefore is an ideal system to study the role of step sites in catalysis in a defined way without having to deal with further complications such as size effects and nanoparticle-support interaction. CO adsorbs initially at step sites before populating terrace sites. CO2 formation observed in TPD experiments indicates that CO dissociation occurs at low coverage at 120 K at the step sites. This is the first report on CO dissociation at a palladium surface. Further, this finding is in surprising contrast to literature data on CO adsorption at 300 K for which no CO dissociation has been reported. The literature data were confirmed by own experiments at 300 K and will be compared to 120 K data. q 2004 Elsevier B.V. All rights reserved