TY - JOUR
T1 - Thermochemistry of Na-faujasites with varying Si/Al ratios
AU - Petrovic, Ivan
AU - Navrotsky, Alexandra
N1 - Funding Information:
We thank Prof. M.E. Davis of CalTech and Dr. J. Cook of Tosoh, USA, for providing the samples of dealuminated faujasites, and M. Simpson of Princeton University for help with the synthesis. We also thank Dr. S. Schramm and C.E. Chase of Mobil Research and Development Co. for collecting the MAS-NMR spectra, and M. Borcsik from Princeton University for ICPES analysis. This work was supported by the US Department of Energy (Grant DE-FG 02-85ER13437) and by the New Jersey Commission on Science and Technology.
PY - 1997
Y1 - 1997
N2 - The thermochemical stability of dehydrated sodium faujasites, NaxAlxSi(1-x)O2, with Si/Al ratios of 1.25 to 360 (x = 0 to 0.44) has been studied by high temperature solution, drop solution, and transposed temperature drop calorimetry near 977 K. Enthalpies of solution become more endothermic as the Si/Al ratio decreases, implying an exothermic (stabilizing) enthalpy of the charge coupled substitution Si4+→Al3 + Na4 in these structures. Deviation of the sample with Si/Al = 1.25 (13X) from the linear trend suggests that there may be a maximum stabilization for the composition with Si/Al = 1. These observations are consistent with previous studies of charge coupled substitutions in aluminosilicate glasses and dense sodium aluminosilicates. Using enthalpies of solution of SiO2, Al2O3, Na2O (derived from Na2CO3 drop solution experiments) and NaAlO2, standard molar enthalpies of formation of dehydrated framework structures from elements, simple oxides, and NaAlO2 and SiO2 were determined. Implications for the synthesis of high silica materials and the apparent thermal stability are discussed.
AB - The thermochemical stability of dehydrated sodium faujasites, NaxAlxSi(1-x)O2, with Si/Al ratios of 1.25 to 360 (x = 0 to 0.44) has been studied by high temperature solution, drop solution, and transposed temperature drop calorimetry near 977 K. Enthalpies of solution become more endothermic as the Si/Al ratio decreases, implying an exothermic (stabilizing) enthalpy of the charge coupled substitution Si4+→Al3 + Na4 in these structures. Deviation of the sample with Si/Al = 1.25 (13X) from the linear trend suggests that there may be a maximum stabilization for the composition with Si/Al = 1. These observations are consistent with previous studies of charge coupled substitutions in aluminosilicate glasses and dense sodium aluminosilicates. Using enthalpies of solution of SiO2, Al2O3, Na2O (derived from Na2CO3 drop solution experiments) and NaAlO2, standard molar enthalpies of formation of dehydrated framework structures from elements, simple oxides, and NaAlO2 and SiO2 were determined. Implications for the synthesis of high silica materials and the apparent thermal stability are discussed.
KW - Calorimetry
KW - Enthalpy
KW - Faujasite
KW - Framework
KW - Stability
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U2 - 10.1016/S0927-6513(96)00060-0
DO - 10.1016/S0927-6513(96)00060-0
M3 - Article
AN - SCOPUS:0031099567
SN - 0927-6513
VL - 9
SP - 1
EP - 12
JO - Microporous Materials
JF - Microporous Materials
IS - 1-2
ER -