Influence of Step Sites on Thermal Behavior of NO on Stepped Pd(112) Studied by AES, XPS and UPS

Abstract

The adsorption and thermal dissociation of nitric oxide on a stepped Pd(112) surface has been investigated by Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). NO undergoes molecular adsorption on a stepped Pd(112) surface at 300 K. With increasing temperature, some NO adsorbed on the surface desorbs molecularly and the remaining NO starts to dissociate into nitrogen and oxygen. The NO dissociation takes place preferentially at the step sites. All NO molecules adsorbed on the surface dissociate above 423 K. Nitrogen desorbs from the surface above 700 K but oxygen exists on the surface or subsurface. UPS results show that the peak at 11.2 eV below Fermi level (EF), originating from the 1π+5σ orbital of NO adsorbed on step sites of Pd (112), disappear at a lower temperature than does the peak of NO adsorbed on terrace sites. This indicates that NO molecules adsorbed on step sites are dissociated at a temperature lower than those at terrace sites. The dissociation activity of NO on Pd(112) is stronger than on the (111) and (110) surfaces, but weaker than on the (100) surface. The order of the dissociation activity is Pd(100) > Pd(112) > Pd(111) > Pd(110).