Adsorption characteristics of a fully exchanged potassium chabazite zeolite prepared from decomposition of zeolite Y

In this work a comprehensive study was undertaken to characterize the porous nature of a fully exchanged potassium chabazite zeolite (KCHA) and evaluate its adsorption properties under different conditions. A synthetic chabazite was prepared from the decomposition of zeolite Y and ion-exchanged to produce a fully exchanged potassium chabazite with Si/Al ratio of 2.4. In addition, sodium chabazite (NaCHA) and lithium chabazite (LiCHA) were synthesized for comparison purposes. Equilibrium isotherms for N2 and CO2 were measured at 273 K for further characterization. Our results show that the porous structure characterization by N2 at 77 K and Ar at 87 K following the standard methods of BET for surface area, t-plot, DR and DFT for pore size distribution and volume reveal pore blockage phenomenon with substantially diminished adsorption capacities. However, CO2 adsorption capacity on KCHA at 273 K reveals magnitudes of 70.1% and 78.7% of those on LiCHA and NaCHA, and a DFT pore volume of 0.214 cm3 g−1. The surface area of KCHA calculated from the CO2 isotherm using the Tóth model in its revised form demonstrates a surface area of 584.4 m2 g−1. This is in contrast to 17.82 and 13.48 m2 g−1 obtained from the BET model using N2 and Ar at 77 and 87 K, respectively. It was concluded that the reliability of standard methods (viz. BET using N2 at 77 K) for characterizing these particular porous solids is questionable under certain circumstances leading to misevaluation of adsorbent properties.