Calculations of the site specific stretching frequencies of CO adsorbed on Li+/ZSM-5

Abstract

Interaction of the CO molecule with Li⁺ within ZSM-5 was investigated by means of the combined quantum mechanics/interaction potential function method. Both, C-on and O-on species were considered. The scaling method based on the linear correlation between CO bond length and stretching frequency has been applied to calculate CO frequencies in CO(OC)–Li⁺/ZSM-5 adsorption complexes. Three types of C-on adsorption complexes with different r(CO) bond lengths, ν(CO) frequencies, and CO binding energies were identified. The calculated IR spectra of CO adsorbed on the Li⁺/ZSM-5 system show three distinctive bands at about 2194 cm⁻¹, 2187 cm⁻¹ and 2183 cm⁻¹ for C-on complexes and at about 2116 cm⁻¹, 2114 cm⁻¹ and 2104 cm⁻¹ for O-on complexes, in excellent agreement with experimental data. Calculated adsorption energies and CO stretching frequencies were used for the simulation of the IR spectra at various CO coverages.