Chabazite structures with Li+, Na+, Ag+, K+, NH4+, Rb+ and Cs+ as extra-framework cations

•Unit cell volumes of chabazites vary with decreasing ion selectivity based on standard free hydration energies of exchange.•Occupancy of cations in different secondary building units is established using synchrotron X-ray powder diffraction.•Infra-red spectroscopy allows assignment of major vibrational bands.

Chabazites with Li+, Na+, Ag+, K+, NH4+, Rb+, Cs+ as monovalent extra-framework cations have been prepared from natural chabazite (ORI-CHA, Ca1.6Na0.5Si8.4Al3.6O24·14.3H2O) and characterized using a combination of Rietveld analyses of high-resolution synchrotron X-ray powder diffraction data and synchrotron infrared (IR) spectroscopy. All monovalent cation-exchanged chabazites crystallize in the rhombohedral space group R3¯m; Li-CHA (Li2.9Si8.6Al3.4O24·13.2H2O), a = 9.4068(6), α = 94.9156(9); Na-CHA (Na3.4Si8.6Al3.4O24·11.4H2O), a = 9.4216(3), α = 94.0773(6); Ag-CHA (Ag3.5Si8.5Al3.5O24·15.9H2O), a = 9.4402(4), α = 94.1354(9); K-CHA (K3.2Si8.7Al3.3O24·10.7H2O), a = 9.4420(1), α = 94.2540(3); NH4-CHA ((NH4)2.1Si8.4Al3.6O24·11.6H2O), a = 9.4378(9), α = 94.6101(1); Rb-CHA (Rb4.1Si7.9Al4.1O24·6.5H2O), a = 9.4318(4), α = 94.533(1); Cs-CHA (Cs3.4Si8.6Al3.4O24·6.4H2O), a = 9.4447(4), α = 94.2604(8). We establish correlations between the unit-cell volume, extra-framework cation distribution, and cation selectivity in chabazites. We establish that the unit cell volume of monovalent-cation exchanged chabazites decreases in the order of decreasing ion selectivity, based on the standard free hydration energies of exchange i.e., Cs+ > K+ > Ag+ > Rb+ > Na+ > Li+ and not the cation size.

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