Adsorption characteristics of divalent cation-exchanged ETS-4s pretreated at different temperature

Divalent cation-exchanged ETS-4 such as Ca2+, Sr2+, and Ba2+ was successfully prepared via ion exchange process. TPD analysis for CO2 shows two distinct peaks based on 187 degrees C. As the pretreatment temperature increased from 200 degrees C to 250 degrees C in TPD analysis, the amount of desorbed CO2 from high peak (i.e. oxygen basic site) was decreased while that from low peak (i.e. M2+-CO2 interaction) was a little increased. Unexpectedly, the amount of CO2 adsorbed on cation site for Ca-ETS-4 was the lowest despite that the electronegativity of Ca2+ is the largest. It is attributed to possible shielding of small cation by the first few molecules of a cavity. The decrease of % change in the amount of CO2 adsorbed on oxygen basic site with the increase in pretreatment temperature for Ca-ETS-4 was most significant arisen from weak basicity of oxygen basic site due to small electronegativity of Ca2+ compared to other two cations. In case of large cation, Ba-ETS-4, however, the increase of % change in the amount of CO2 adsorbed on cation site was most significant due to less shielding effect as well as higher degree of dehydration of Ba2+. The adsorption of CO2 using BET apparatus was well consistent with that of a single adsorption capacity using gravimetric method. (C) 2011 Elsevier Inc. All rights reserved.