Thermochemistry of formation of ion exchanged zeolite RHO

Zeolites Na,Cs-RHO, Cd,Cs-RHO, and Li,NH4-RHO were synthesized in an aqueous ion-exchange media and studied by powder X-ray diffraction. Their thermochemistry was investigated by differential scanning calorimetry and high temperature oxide melt solution calorimetry. The formation enthalpy from binary oxide components of hydrated zeolite RHO varies linearly with the average ionic potential (Z/r) of the extra-framework cations and ranges from -34.46 +/- 0.52 kJ/mol for Na,Cs-RHO to -16.75 +/- 0.57 kJ/mol for Cd,Cs-RHO. The formation enthalpies for dehydrated zeolite RHO range from -25.49 +/- 0.64 kJ/mol for Na,Cs-RHO to +4.12 +/- 0.99 kJ/mol for Li,NH4-RHO. These values do not vary linearly with average ionic potential but do show a linear relationship with distortion parameter.