TY - JOUR
T1 - Formation and dehydration enthalpies of gallosilicate materials with different framework topologies and Ga contents
AU - Zhou, Wei
AU - Sun, Pingping
AU - Navrotsky, Alexandra
AU - Kim, Seok Han
AU - Hong, Suk Bong
N1 - Funding Information:
We thank Sean Mulcahy and Sarah Roeske for microprobe analysis. This work was supported by US National Science Foundation, Grant DMR 0601892 and Korea Science and Engineering Foundation through the National Research Lab program (R0A-2007-000-20050-0).
PY - 2009/5/1
Y1 - 2009/5/1
N2 - A series of gallosilicate materials with different framework structures (i.e., Ga-MAZ, Ga-OFF, Ga-MOR, TNU-6, and TNU-7) and different Ga contents is investigated by high temperature solution calorimetry in molten lead borate at 700 °C. The dehydration enthalpies for the fully hydrated samples transforming to the partially dehydrated samples, which have 10-20% of the original amount of water remaining, lie in the range 2.0-14.6 kJ per mole of TO2 (T = Si or Ga) and 4.3-24.1 kJ per mole of H2O. The formation enthalpies from oxides of fully hydrated samples range from -87.9 to -4.8 kJ per mole of TO2, while the formation enthalpies of anhydrous samples are estimated to range from -87.9 to +9.8 kJ per mol TO2. The dependence of enthalpies on the framework density and Ga/(Ga + Si) ratio is examined. Similar to trends in aluminosilicate zeolites, high framework density, high T3+ content and large charge balancing cations stabilize gallosilicate materials. Enthalpies of vitrification of gallosilicate crystals are estimated by integrating differential scanning calorimetry (DSC) peaks, and formation enthalpies of gallosilicate glasses are calculated.
AB - A series of gallosilicate materials with different framework structures (i.e., Ga-MAZ, Ga-OFF, Ga-MOR, TNU-6, and TNU-7) and different Ga contents is investigated by high temperature solution calorimetry in molten lead borate at 700 °C. The dehydration enthalpies for the fully hydrated samples transforming to the partially dehydrated samples, which have 10-20% of the original amount of water remaining, lie in the range 2.0-14.6 kJ per mole of TO2 (T = Si or Ga) and 4.3-24.1 kJ per mole of H2O. The formation enthalpies from oxides of fully hydrated samples range from -87.9 to -4.8 kJ per mole of TO2, while the formation enthalpies of anhydrous samples are estimated to range from -87.9 to +9.8 kJ per mol TO2. The dependence of enthalpies on the framework density and Ga/(Ga + Si) ratio is examined. Similar to trends in aluminosilicate zeolites, high framework density, high T3+ content and large charge balancing cations stabilize gallosilicate materials. Enthalpies of vitrification of gallosilicate crystals are estimated by integrating differential scanning calorimetry (DSC) peaks, and formation enthalpies of gallosilicate glasses are calculated.
KW - Dehydration enthalpy
KW - Formation enthalpy
KW - Framework density
KW - Gallosilicate materials
KW - TG-DSC
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U2 - 10.1016/j.micromeso.2009.02.001
DO - 10.1016/j.micromeso.2009.02.001
M3 - Article
AN - SCOPUS:61849120220
SN - 1387-1811
VL - 121
SP - 200
EP - 207
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
IS - 1-3
ER -