Simulated annealing effects on Na-FAU crystal reconstruction and sorption efficiency

Panagiotis Krokidas (1) , Eugene D. Skouras (2) , Vladimiros Nikolakis (2) , Vasilis N. Burganos (3)

1 Dept. of Materials Science
2 ICE-HT
3 ICE-HT

The accurate reconstruction of zeolite frameworks at the atomic scale is of critical importance for the study of the sorption and separation properties of these materials. In this work, the atomistic description of NaX FAU crystals is accomplished using lattice reconstruction and simulated annealing techniques. The effect of temperature on the NaX framework structure and on the precise positioning of the extra-framework cations have been thoroughly investigated using annealing cycles at several temperatures. The effects of the framework details including the cation positions on the sorption of CO2 and N2 in these structures are studied using molecular simulations. Comparison of simulated adsorption isotherms in non-annealed structures to experimental data reveals that the agreement is a strong function of the cation positions in the framework. More consistent results are obtained when annealing is performed, in which case the deviation in the energy calculations is reduced by almost two orders of magnitude. Cation tracking during several annealing cycles is also implemented that reveals the existence of strongly preferred positions for cations close to the Al atoms within the super cage. Comparison of the calculated and experimental values for the heat of adsorption obtained in this work reveals satisfactory agreement in both CO2 and N2 sorption cases for structures that have undergone simulated annealing.

Mots clés: Physical Sciences

Panagiotis Krokidas, Eugene D. Skouras, Vladimiros Nikolakis, Vasilis N. Burganos. Simulated annealing effects on Na-FAU crystal reconstruction and sorption efficiency. Molecular Simulation, 2008, 34 (10-15), pp.1299-1309. ⟨10.1080/08927020802208950⟩. ⟨hal-00515039⟩