In Situ Fourier-Transform Infrared Spectroscopy Study of Carbon Monoxide Adsorption on Silver Nanoparticles Contained in BETA Zeolite Nanocrystals

Silver nanoparticles dispersed in/on BEA zeolites were characterized by CO adsorption at room temperature, followed by in situ FTIR spectroscopy. The behavior of the cationic silver containing BEA sample was analyzed after calcination, following two distinct reduction procedures: a wet chemical reduction by triethylamine and a dry in situ chemical reduction by H₂ gas. A prominent band located at 2190 cm^-1 appeared in the FTIR spectra following CO adsorption on the reduced samples that corresponds to the vibrational frequency ν(Ag⁺-CO). The absence of the Ag⁰-CO band and the presence of the Ag⁺-CO band concomitant with the simultaneous detection of CO₂ and carbonate species were attributed to the Boudouard reaction that proceeds through dissociative CO adsorption on Ag nanoparticles. Besides, the dispersion of Ag⁺ was evaluated from the evolution of the band at 2160-2210 cm^-1 that is characteristic of the Ag⁺-CO vibrational mode. This study describes the reaction behind the conversion of CO to CO₂ on silver nanoparticle sites in the absence of oxygen via assigning and analyzing the spectral responses obtained in order to understand the chemical activity of silver species occurring at the interface of BEA nanocrystals that are obtained by different pretreatment methods.