Semi-empirical calculations of the vibrational frequency of carbon monoxide adsorbed on noble metal single-crystal surfaces

P.A.Paredes Olivera,E.P.M Leiva

doi:10.1016/0022-0728(93)80224-6

P.A.Paredes Olivera, E.P.M Leiva

Open Access

https://doi.org/10.1016/0022-0728(93)80224-6

Copy DOI

Abstract

In this work we perform a theoretical analysis of the shift of the observed IR reflection—absorption spectroscopy (IRRAS) band of CO adsorbed on Pt(111), Rh(111) and Pt(100) single crystals as a function of both the degree of CO surface coverage and the electric potential applied at either the metal—vacuum or the metal—solution interface. The wavefunctions obtained using a modified extended Hückel molecular orbital (EHMO) method are used to predict the vibrational frequency data. The Pt(110), Rh(111) and Pt(111) single crystals are modelled by bilayer clusters of 25 and 22 atoms respectively. A theoretical description of the observed IRRAS shift is analysed by means of a population analysis of CO molecular orbitals, which confirms the donation—back-donation model.

Highlights

The chemisorption of CO on noble metals such as Pt and Rh in aqueous solution is of particular interest in relation to Cl chemistry [l-6] because CO acts as a poison in the catalytic electro-oxidation of a number of organic compounds such as methanol, formic acid and hydrocarbons through the occupancy of substrate active surface sites [7,8]
In this work we perform a theoretical analysis of the shift of the observed IR reflection-absorption spectroscopy (IRRAS) band of CO adsorbed on Ptflll), Rh(ll1) and Pt(100) single crystals as a function of both the degree of CO surface coverage and the electric potential applied at either the metal-vacuum or the metal-solution interface
The use of vibrational spectroscopic probes to characterize small adsorbates at ordered monolayer surfaces in an ultrahigh vacuum (UHV) provides valuable structural information about surface systems, and in this respect the application of JR reflection-absorption spectroscopy (IRRAS) to metal-solution interfaces involving well-ordered single crystals provides an opportunity for in-situ characterization of these systems [ll-141

Summary

Introduction

The chemisorption of CO on noble metals such as Pt and Rh in aqueous solution is of particular interest in relation to Cl chemistry [l-6] because CO acts as a poison in the catalytic electro-oxidation of a number of organic compounds such as methanol, formic acid and hydrocarbons through the occupancy of substrate active surface sites [7,8]. The electro-oxidation mechanism of CO adsorbed on Pt and Rh low Miller indexed surfaces has recently been interpreted at the atomic level in terms of. The shifts in the vibrational spectra of some adsorbates in UHV and in the electrochemical environment have been related to the influence of the solution phase on the adsorption process [15,X]. The use of the extended Hiickel molecular orbital method (EHMO) has been employed to study the stability of CO, H and 0 on Ni(ll1) surfaces [25]. In this case a linear correlation between the C-O stretching frequencies 5 and the square root of the overlap population P has been obtained

Results

Discussion

Conclusion