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 N-2 and CO2 were measured at 273 K for further characterization. Our results show that the porous structure characterization by N2 at 77 K and At 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 cm(3) g(-1). The surface area of KCHA calculated from the CO2 isotherm using the Toth model in its revised form demonstrates a surface area of 584.4 m(2) g(-1). This is in contrast to 17.82 and 13.48 m(2) g(-1) obtained from the BET model using N-2 and At at 77 and 87 K, respectively. It was concluded that the reliability of standard methods (viz. BET using N-2 at 77 K) for characterizing these particular porous solids is questionable under certain circumstances leading to misevaluation of adsorbent properties. (c) 2008 Elsevier Inc. All rights reserved.