Macroscopic and Molecular Insights from CO Adsorption on NaY Zeolite: A Combined FTIR and Manometric Study

Abstract

This survey combines both quantitative and IR molecular descriptions and aims to provide new insights for the description of CO adsorption on NaY zeolite at 77 K. Quantitative measurements of the number of CO molecules trapped in the microporous super cage are compared to the corresponding IR spectra of CO as adsorbed species. We demonstrate that polycarbonyls formed during the completion of the accessible SII Na+ coordinative vacancies result in the formation of mono-, di- and tricarbonyls but not consecutively. Quantitative analysis and measurements of the CO molecules that are adsorbed prove that polycarbonyls coexist with different proportions over the adsorption step in line with previous theoretical prediction.(1) Moreover, we establish that polycarbonyl formation settles rapidly and stops, although the completion of the SII Na+ coordinative vacancies has not been fully achieved. The formation of CO in the pseudoliquid phase causes this adsorption limitation, and distinction within adsorbed species must be made between species that are truly Na+-coordinated and those that are adsorbed in a condensed state in the confined micropores. As a result, this combined analysis reveals that the sole manometric measurements resulting in the macroscopic CO isotherm overestimate the number of “true” coordinated species.