FTIR study of the interaction of CO with pure and silica-supported copper(I) oxide

A comparative FTIR spectroscopic study of CO adsorption on Cu2O and on silica-supported Cu2O microcrystals has been carried out in order to investigate the relations between the IR spectrum of adsorbed CO and the morphology of the particles las obtained by SEM and TEM analyses). Modelling of the crystal morphology was also performed by means of atomistic simulations. and the results were compared with the electron micrographs. On both samples, CO adsorption occurs on Cu(I) ions located on the predominant and unpolar (111) faces. The simultaneous presence in the IR spectra of adsorbed CO of two components at 2158 and 2162 cm(-1) tweak and fully reversible) and at 2127 and 2132 cm(-1) (strong and quite irreversible), which shift downward of about Delta<(nu)over bar>congruent to - 8-10 cm(-1) and Delta<(nu)over bar>congruent to - 12-13 cm(-1), respectively, as a consequence of the progressive building up of lateral interactions within the bidimensional phase, is explained in terms of two alternative models. The first model explains the presence of the two IR bands in terms of CO adsorption on the two different Cu(I) sites (mono and bicoordinated) present on the (111) face of Cu2O Following the second model, the observed IR doublet is on the contrary associated with the formation of Cu(I)(CO)(2) species on monocoordinated Cu(I) sites. On the basis of the calculated electric field at the two surface sites of the relaxed and unrelaxed (111) Faces, the second model seems to be more appropriate. (C) 1998 Elsevier Science B.V. All rights reserved.