FTIR study of CO and NO adsorbed on nitrided CoMo/Al2O3 catalysts

The states of surface Co and Mo sites on nitrided CoMo supported on Al2O3 were studied by adsorption of CO and NO as IR probe molecules. Three IR bands at 2200, 2060 and 2025 cm(-1) were detected for adsorbed CO. These bands can be respectively attributed to the surface NCO species as a result of CO adsorbed on surface N sites, and linearly adsorbed CO on surface Co and Mo sites in low valence states. The addition of cobalt to the Mo nitride diminishes the band at 2200 cm(-1). This may be due to either the change of the surface structure of the supported nitride, or the formation of a new phase, CoxMoyNz, as suggested in the literature Kim et al., Catal. Lett., 1997, 43, 91 and Logan et al., Catal. Lett., 1998, 56, 165. Comparison of CO and NO adsorption on Mo2N/Al2O3 and CoMoNx/Al2O3 indicates that the presence of cobalt can promote the reduction and nitridation of Mo.

Surface-enhanced Raman scattering of xanthopterin adsorbed on colloidal silver

Surface-enhanced Raman scattering (SERS) of xanthopterin adsorbed on colloidal silver was measured and the Raman spectrum calculated by the density functional theory method was also obtained. Xanthopterin can be detected down to 5 X 10(-9) m and the enhancement of the scattering intensity is at least 10(5)-fold. Xanthopterin molecules are adsorbed flatly on the surface of the Ag particles. This study shows that SERS could be another prospective method for the detection of pterines. Copyright (C) 2001 John Wiley Sons, Ltd.

Dissolution kinetics of octadecanethiolate monolayers electro-adsorbed on Au(1 1 1)

Monolayers of octadecanethiolate on Au(1 1 1) surface were formed under electrochemical control. The influence of the formation time on the reductive desorption process was studied by cyclic voltammetry and chronoamperometry. When the formation time is increased, the reductive desorption peak observed on the voltammograms is significantly shifted in the negative direction, while the cathodic charge is only slightly affected. This behaviour is attributed to a higher degree of organisation of the monolayers for longer formation times, highlighting the role of defect sites in promoting the dissolution. A good agreement was found between our experimental chronoamperograms and theoretical models describing the dissolution process by a shrinkage mechanism. It is demonstrated that a reorganisation process takes place, consisting in the merging of small condensed domains into larger ones. This annealing phenomenon is time and potential dependent, the largest condensed domains being obtained for the longest formation times and least negative potentials. © 2008 Elsevier B.V. All rights reserved.