How does CO capture process on microporous NaY zeolites? A FTIR and DFT combined study

International audienceReliable experimental IR and theoretical approaches, both investigating CO adsorption on NaY faujasites, are supporting that CO capture occurs through the completion of the vacant coordination of Na+ cations located in the accessible SII sites. As a result, carbonyl adsorbed species are formed by the capture of one, two or three CO molecules and are experimentally discernable by their respective IR positions that are down-shifted by an average 11-12 cm−1 value for each captured CO molecule. DFT analysis is proposed for comparison and reproduces well the observed experimental shift of the νCO positions of the different polycarbonyls of interest. In addition, the effect of Si or Al composition surrounding the SII Na+ cation is investigated and results suggest that polycarbonyls that are formed might be in connection with the acidic strength of the cationic sites. This combined study completes and improves the understanding of the complex issue of CO adsorption at 80 K widely used as a model to explain how physical adsorption takes place in NaY faujasites working as an efficient industrial adsorbent in gas separation or gas purification processes

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

International audienceThis 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 S-II 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 S-II 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