A quantum chemical study of the decomposition of Keggin-structured heteropolyacids

The Journal of Physical Chemistry. B
Michael J JanikMatthew Neurock

Abstract

Heterpolyacids (HPAs) demonstrate catalytic activity for oxidative and acid-catalyzed hydrocarbon conversion processes. Deactivation and thermal instability, however, have prevented their widespread use. Herein, ab initio density functional theory is used to study the thermal decomposition of the Keggin molecular HPA structure through the desorption of constitutional water molecules. The overall reaction energy and activation barrier are computed for the overall reaction HnXM12O40-->Hn-2XM12O39+H2O. and subsequently used to predict the effect of HPA composition on thermal stability. For example, the desorption of a constitutional water molecule is found to be increasingly endothermic in the order silicomolybdic acid (H4SiMo12O40)<phosphomolybdic acid (H3PMo12O40)<silicotungstic acid (H4SiW12O40)<phosphotungstic acid (H3PW12O40), in agreement with the experimental ordering of their thermal stability. The presence of an adjacent Keggin unit may stabilize the structural defect created by the water desorption, thus suggesting that constitutional water loss is an initial step toward the decomposition into a bulk mixed oxide. The equilibrium concentration of defective Keggin units is determined as a function of temperature and water ...Continue Reading

References

Sep 15, 1988·Physical Review A: General Physics·A D Becke
Oct 15, 1996·Physical Review. B, Condensed Matter·G Kresse, J Furthmüller
Apr 15, 1990·Physical Review. B, Condensed Matter·D Vanderbilt
Jan 1, 1993·Physical Review. B, Condensed Matter·G Kresse, J Hafner
Apr 7, 2005·Journal of the American Chemical Society·Michael J JanikMatthew Neurock

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Citations

Aug 9, 2017·Dalton Transactions : an International Journal of Inorganic Chemistry·A C ColussoA M McDonagh
Aug 7, 2010·Dalton Transactions : an International Journal of Inorganic Chemistry·Fu-Qiang ZhangHai-Shun Wu
Aug 14, 2012·Chemical Society Reviews·Xavier LópezJosep M Poblet
Aug 14, 2012·Chemical Communications : Chem Comm·Pablo Jiménez-LozanoJorge J Carbó
Apr 22, 2011·The Journal of Physical Chemistry. a·Irena Efremenko, Ronny Neumann
Oct 22, 2014·Journal of the American Chemical Society·Prashant DeshlahraEnrique Iglesia
Apr 6, 2007·Langmuir : the ACS Journal of Surfaces and Colloids·Soumyajit RoyWillem K Kegel

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